Step 1: Please use the current password of your Navatar admin account to log into the Sandbox.
Step 2: Click on Avatar Icon on the right side as highlighted below and click on settings.
Step 3: Select "Change My Password" in the Quick Find box on the left. Input the current password for the admin account and enter the new password. Please set the new password as navatar123
Step 4: Click on Save once you have changed the password.