
Do you have an MS 365 subscription? Did you purchase it for yourself or is it provided by your work/school?
If you purchased it yourself then go to the Accounts section in Office. There is an option there on the right side to Manage Account, Switch License and Update License. Ensure you are logged into Office using the MS account that has the subscription and it should detect it. If you are logged in then use Update License to force an update.
If your work/school provides the license then you'll need to reach out to their IT department to ensure that your account has been granted a license. They should be able to help you with that.