Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
In any O365 if functioning, any component > Help > Contact support
If an installation issue (ie you have never been able to install) then what is the exact problem, and what exactly did you purchase?
If it has been installed, the basic repair is;
Restart the PC, once fully loaded, repair Office,> Apps & Features>Select Office your version>Modify /Repair, once the repair completes re-test (Quick repair)
O365 when installed under a Win user admin account, and run from that admin account, auto logs in when the PC is started. There is no separate login for any component.