Step One:

Enable legacy in the Blesta config file:
/config/blesta.php

Configure::set("Blesta.auth_legacy_passwords", false); set it as true.

Step Two:

Then open to blesta database. Go to “user” table and click on “edit” of the user.

Step Three:

Set the Password field as function MD5, and put your desired password.

Step Four:

Go

All done! Now login with username and new password.