How to decode encrypted Wordpress admin password?

You cannot easily decrypt the password from the hash string you see. You are better off replacing the hash string with the new one from the password you know.

It says well here:

https://jakebillo.com/wordpress-phpass-generator-resetting-or-creating-a-new-admin-user/

Basically:

• generates a new hash from a known password, for example http://scriptserver.mainframe8.com/wordpress_password_hasher.php as described in the above link, or any other product that uses the phpass library ,
• use your DB frontend (like phpMyAdmin) to update the user_pass field with a new hash line.

If you have more users in this WordPress installation, you can also copy the hash string from one user whose password you know to another user (administrator).