Re-installing an older version?

Apologies for the repetition: I realise I’ve already asked this question at the end of a bug-report — but it occurs to me you may only read those occasionally!

Usually very upgrade-shy but I took the plunge and upgraded from 3.1.1 to 3.3.1 — and now regretting it! (Kept crashing on me…)… Wondering how to properly downgrade again. For now, I’ve just binned the actual 3.3.1 application & gone back to opening scapple files with my old copy of 3.1.1, but suspect there may be other junk from the upgrade remaining in my system I ought to clean out! Thanks for your help .