After it arrives
If it comes off
Two different problems get mixed up here. A piece that is wrong for the outlet goes back through the retail partner. A cord that will not stay put along the baseboard usually needs nothing sent back at all.
Where a return starts
With the retail partner that sold the piece. The window, the condition the piece has to be in, and the way the money comes back are all set by that listing, and their record is what the process runs on.
Nothing should be posted to the address on the contact page. A box arriving there does not enter any return process and there is nobody at that suite able to put it into one.
The most common reason a piece goes back
The ground pin points the wrong way. The round hole on the wall is at the top and the plate was cut for a wall where it sits at the bottom, or the other way around. The two cannot be swapped or forced, and no adapter fixes it.
This is worth two minutes with a photograph before ordering. Both arrangements exist in this catalog, and the page for each says plainly which wall it belongs on.
If the adhesive let go
Usually the wall is the reason rather than the strip. Pull one off and look at what came away with it. A strip carrying paint flakes means the paint was too fresh. A strip carrying paper means it was on wallpaper. A strip that came away clean was probably on dust.
Wipe the run with rubbing alcohol, let it dry properly, and press the new strip for half a minute rather than a second. On textured plaster, no strip will do the job, and a piece with clips is the better answer.
If something is wrong with the piece itself
Stop using it. A plate that is cracked, a cord with a nick in the jacket, or a body that gets warm in the outlet is a piece that has to come out of the wall before anything else is decided.
Then send a photo to the address on the contact page along with the order number. It will not move the return along by itself, but it tells us what came out of the tooling wrong, and that is how the next batch gets fixed.