unsolve

verb2

1. •
   To undo or remove the solution to a problem; to put something into an unsolved state.

   • “But I cannot allow you to use my cousin to solve or, I suppose, more precisely, to unsolve your case.” — 2001
2. •
   (no longer used) To solve.

   • Perchance, my Fancy would have bin so kinde, / T‘ unsolve the doubts of my perplexed minde. — 1631