Some wanted/required files are missing in some repositories and don't get synced. I think I did not drop these files but this doesn't matter right now. Can I reset the information which files got dropped or getted (hope it's clear what mean) and just tell annex to (re-)distribute the files according groupwanted/wanted/required?
If I understand you correctly you mean that you somehow got git-annex' location tracking out-of-sync with the reality of where files are? I.e.
git annex list
shows some files as present in a repository which aren't actually there?If yes then
git annex fsck
(https://git-annex.branchable.com/git-annex-fsck/) should find and correct these issues (or tell you if they are not fixable).