It’s pretty simple I’m going to show you how to do that , Right click on Computer icon and choose device manager .
Now Click on Local User and Group
You must be seeing Administrator Account here , right Click on Administrator and choose Set Password
You will see Password Prompt to set , Then Click on Proceed
Put Your desirable Password here For administrator And then press Ok
Now you administrator password is set Now reboot the system and check it will open with the new password.