How to apply adhesive when reassembling device?

For the purposes of sealing the phone as well as possible, I always prefer using pre-cut adhesives rather than tape that you have to trim to fit. I poked around a bit and it seems the adhesive for your particular phone isn't exactly in great supply. On Amazon all I could come up with were replacement back covers that come with adhesive, although to be honest the price wasn't all that bad - around $12 USD.

The adhesive guide referenced in the daughterboard guide should work fine for installing your precut adhesive if you end up getting some. Just make sure to clean both surfaces really well with high purity isopropyl alcohol (not the normal 70% stuff we usually have around the house).

The adhesive pretty much always gets applied to the phone itself, not the cover. Check the shape and match it up to where it's going to sit to make sure you get it in the right orientation. When you go to fit it, make sure all the connectors and cables and everything are laying flat so the adhesive will sit in place correctly.

Once you've peeled the backing and put the adhesive in place run around the edges with the flat side of a spudger and press it firmly into place so it won't come up when you peel the rest of the backing off.

That's about it; if you have any questions feel free to ask.

Best of luck with your repair!

EDIT: I found a couple of listings for the adhesive on eBay, but both sellers were out of stock so I didn't mention them. However, it occurs to me that you can look at the listing to see exactly where the adhesive actually goes so if you wind up using the Tesa tape you'll have a guide to go by. Here's a picture from the listing that might help.

Here's the listing it came from, just in case you want to contact them and see if they plan on getting any more in stock.

Motorola Moto G7 / G7 Power LCD Adhesive Sticker Tape Repair Tool 1 or 2 Pcs