Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
If you have a perpetual license, you may run into activation issues after certain hardware changes have been made on the computer. You may have to contact Microsoft support for assistance with (re-)activation.
If you actually got a new computer and a perpetual version of Office was preinstalled on the old one, talk to the seller and find out how they can help.