This question comes up semi-often on our Discord chat server, and while we don't have an official recommendation, this is the general rule of thumb we have pinned there for folks to recommend to one another: https://i.imgur.com/MnTAVfs.png

While I definitely wouldn't recommend restarting entirely, reviewing the material from start to finish and focusing your time first on practicing those exercises with sessions dedicated to what would usually be our warmups is a good way to refresh your memory before resuming where you left off.