You can't easily decrypt the password from the hash string that you see. You should rather replace the hash string with a new one from a password that you do know.
There's a good howto here:
https://jakebillo.com/wordpress-phpass-generator-resetting-or-creating-a-new-admin-user/
Basically:
If you have more users in this WordPress installation, you can also copy the hash string from one user whose password you know, to the other user (admin).