I want to recover my wallet since I forget my encryption password, for this I am trying to import the wallet with the 12 words and the system gives me an "error" and the message "already this wallet exists". What should I do?
First, use your 12 words to import the wallet to another device. Once you have successfully done this, you should be able to delete the wallet from your original device, then re-import it.
I always recommend importing to another device first before deleting the original wallet, just in case the import has issues.