How to reset my puzzle rating?

When did you achieve the 85? There was a bug one day when the progression system was broken and you got nothing but trivial backrank puzzles to no end.

Lichess removed some of the 100+ scores that were achieved on this day by request.

If this wasn't the case, then just keep the 85 and deal with it?

That's interesting! Thanks for pointing it out. I can't remember that, but I was hoping somebody could run a script across the database to check for this and similar known aberrations. I mean it defeats the idea of score-keeping if the numbers aren't representative of actual and current skill. I'm just hoping they will make it so this rating too can drop, like most of the others can, and usefully so.

not possible, sorry