How to change the back camera glass of moto G5plus?

As far as known Motorola does not provide or sell any replacement parts for its devices. To fix your problem, it is recommended to take your device for repair. Generally these type of components are not under warranty, so it is most likely, that the service center might ask for a fee to repair it.
Apart from it, if you can get a rear camera from somewhere you can follow these steps and check out if it works. You need these following tools to work with:
a) Torx screwdriver T3, b)Spudger and 3)Tweezers

1. Remove back cover
2. Remove rear housing
3. Remove motherboard
4. Remove the adhesives underneath carefully, by peeling them off one by one.
5. Remove rear camera glass
6. Install the new rear camera glass
7. Install back the motherboard with the help of the above said tools. You have to be extra careful while peeling off the black stickers and while placing them back.
8. You have to gently take out the wires and place them back.
9. Place the rear housing back to its place.
10. Place the back cover and you are done.

Even I have the same problem with my camera. There is a single line on the rear camera glass. I even ordered a glass and have it with me. But, just like Anwesha said, it would be a good idea to get it replaced by the local repair center.
I even went through a couple of video tutorials on YouTube, but cannot bring myself to change the glass for the fear of damaging the camera, or the phone itself.
However, if you have the technical knowledge of the stuff, you can try it. The glass may not be available in India. Search online to see if it is available overseas. I got the glass for my phone from such online trader as I could not find the glass at the local Samsung service center ( My phone is a Samsung Galaxy).

I think most of the people would have experienced this problem. At the rear camera, there is an outer glass and an inner lens provided together. You have mentioned that your images are blurring. So the problem might be on the glass only. In local shops, you can ask about the back glass. But for Motorola, parts are not simpler to get from outside. According to me don't take a risk by manually solving this problem. Contact the Motorola service provider or get into the local service shop. They will solve your problem.
This is a sensitive issue. If you try to open the back glass, there is a possibility of the lens getting damaged. Suppose if the lens gets affected, you need to change the entire rear camera with a huge amount by investing in it. The technical people handling this issue will be better. Don't take any risk in this situation.

Considering the Moto G5 Plus phone, it requires you to dismantle the camera unit from the rest. I think it'd be wise to give it to the service center. This way you can get it replaced through repair person in the service center. It is possible to do it yourself, but if the phone is within the warranty then it makes sense to do it through the service center.

For manual installation, it'd be good if you check out the below youtube video series.
https://www.youtube.com/watch?v=mKtAaniGGbU

Aliexpress has the Moto G5 Plus camera glass that you can buy online. You may also order the same from the other franchise of the Motorola. You may have to pay that respective price.
Check the following URL : https://www.aliexpress.com/popular/moto-camera-glass.html

There are two solutions for your problem:-
1. Get the rear camera glass replaced by visiting the customer care.

2. Inquire online and offline for the real camera glass of your phone and replace it by yourself using the methods as Anwesha mentioned above.

I had found some rear camera glasses that are available online :-
1. OEM Camera Lens Glass Cover For Motorola G5 Plus
Price : Rs 495 on Ebay India
2.New Camera Glass Lens Cover for Motorola Moto G5 Plus
Price Rs 349 on Ebay India
3. OEM Camera Glass Lens for Motorola Moto G5/G5 Plus
Price US$3.41 on Witrigs (Lowest Price and you'll get lens around 20-50 days )

If you can replace it by watching the various Youtube tutorials available online the order one glass and replace it by yourself. If you does't need to take the risk then you can go to the nearest service center and get it replaced . They'll charge you for that even your phone is in warranty.

It's a common problem of getting the camera glass broken or having a scratch on it. To avoid these type of scratches or damages I should suggest you to go for using back cover. These problem generally occur to those phone which has the back camera a little bulged out. To save your future money you can use these suggestions.