Don't know how to set new administrator

[handbagdraft]

I have a laptop from my ex-colleague who has Administrator rights and a OneDrive account set as default. I tried to add a new user, but it requires signing into a Microsoft account, and the only option is my ex-colleague's account. How can I change Administrator rights without logging into the existing Administrator account? Should I contact my ex-colleague to add a new user, and then remove the old Administrator once I'm set up as the new Administrator?

 

[Bighorn]

Should I contact my ex-colleague to add a new user, and then remove the old Administrator once I'm set up as the new Administrator?

That would be the "legal" way to do it. Another is to activate the hidden Administrator to create the new User or change a Standard account to Admin but be sure to change the hidden back, not good to leave it active.
To make it visible so as to fix the problem in a Command Prompt window type
SET USER ADMINISTRATOR /ACTIVE:YES
Reboot to fix things then when finished type
SET USER ADMINISTRATOR /ACTIVE:NO then reboot. It's wise not to routinely use that hidden account.