Obtain a rice cooker or something similar (got mine from a thrift shop, don't use it for anything else), 3d printed pieces, chemicals, metal plate, and a stand off. I used PLA and PETG with acetone, MEK, xylol, and TRPS.
Step 1: Boil the Chemicals
First you should definitely do this outside and if possible wearing a respirator, although I have once in a while done this inside also personally I don't have a respirator but don't be like me. Pour about 1/4" of the desired chemical into the cooker about, place the plate on the standoff, place a piece on the plate and then boil chemical for about 20-60 secs after you see vapor.
Step 2: Results
So TRPS worked for PLA eventually after pouring extra and boiling it longer and nothing else really worked, except for acetone and PETG somewhat.
Acetone didn't do much for pla except make it dull looking and dissolve some component, but for petg it made it shinny and maybe a a very little smoother, the bumps from retraction are still there. MEK did the same thing as acetone for PLA except more, dull and something dissolved and seems like wax, for PETG it was also similar to acetone but duller. TRPS (Turpentine Replacement Paint Solvent) had potential since the bottom of my first try seemed smoothed so I tried again and it worked too much this time since I had it in there a while to make sure whether or not it would work. for PETG it became softened and deformed but not really smoothed it seemed like the chemical permeated the plastic. Xyolol dulled both PLA and PETG and seemed to smooth PLA a little bit (which accidentally slid off the plate and into the liquid). Naptha did abosultely nothing for PLA and for PETG made it shinny and seeped inside and expanded it a bit.