Hello and welcome to this forum.
Alas, you won't find much support for a third-party RetroPie installation here, because we can't know how much its makers changed the official installation image. On top of that, RetroPie's licence and the licences of many of its components don't allow commercial use, including selling it as part of a commercial product. The people who sold it to you broke those licences.
So, you'll have to either ask the vendor about the problems with their product, or install the official image from https://retropie.org.uk/download/. In the latter case, you should make a backup of your old system and its games as described here – or just use another SD card.
We'll be happy to help you with any problems you may have with the official image. As a side effect, you may learn a bit or two about the inner workings of the wonderful retrogaming box of bricks that RetroPie is. 👍
Be sure to read https://retropie.org.uk/forum/topic/3/read-this-first to get more useful information to start in this forum.