I assume ur friend used cupramine which wont be absorbed by silicon or leave a residue.
Big water changes >80% and run carbon, lots of carbon. The copper level will drop but depending on how much copper the LRs has absorbed, it could be a long process to totally remove the copper.
either that, or change out all the LRs. but the fishes will be affected this way as the new LR could trigger a new cycle.
Its certainly possible as I just did it. Once the test kit show that copper is zero, dont trust it. do a couple more water changes, one more round of new carbon, then throw a few snails to see if they can survive.
If survive, then slowly add easy corals to test.
Good luck