I fixed some wrong notes in a custom song myself but the game still wont recognize the new version. I heard that clearing out that songs cache will fix it but i don't know how to do that.

One reason that the game wouldn't "recognize" the new version is if you still have the old one in the folder. So make sure you've taken the old one out.

In most cases, your progress/scores on the previous version will carry over to your new version, so try playing the version that shows up in RS. It might actually be your updated version.