You need the password to decrypt it. If you don't know the exact password but have some idea of what it might be you can attempt to bruteforce it. That means to try various combinations of passwords until you hit the right one. You can bruteforce it using btchris' script given below or hire someone to do it for you:

https://github.com/gurnec/btcrecover

However you must have at least some idea of what the password might be for bruteforcing to be feasible.