First obvious thing is to try and reset your password, but if that does not work, you can login into PhpMyAdmin, locate the mailwizz database and in it, the user table (ss_user if you used the ss_ prefix).
The user table will contain a column for password.
Edit that column and in it put following string:
This is the password hash for:
Now save your changes and try to login in the application backend by using this password, you should be able to do it successfully.
After login, simply change your password from your account area (right under the avatar logo).