There is no way that moving a thrust line down would increase lift due to prop wash hitting the bottom of the wing. It's not physically possible for that to happen.

The OP probably shouldn't go modifying his plane just yet. Assuming the plane is in the configuration that the factory built it in, it's probably close to being like it needs to be. As I mentioned above, the plane is probably not trimmed right to start with. It's normal for a trainer to rise and fall a bit with speed changes, but not as much as the OP is describing.

The much smarter next step for the OP is to do some measuring. Measure the CG and compare it to where the manual says it should be. Measure the thrust lines, both vertical and horizontal to see where you are. That way we won't be taking a shot in the dark to try and help you. And if you haven't already, do a search for local clubs to try and find an experienced pilot to help you. If I were local to you, I could take your plane up and know within the first 10 seconds of flying what it needed. That's a lot better than taking days to get best guesses from strangers on a forum and possibly making the problem worse.