Hi @Lorne Andersen ,
Welcome to Q&A Forum!
According to my research, there is no OOTB way to automatically fill in the Office location based on the User Name in SharePoint Online.
You can use Microsoft Flow to achieve your needs. Please refer to the below workaround:
1.Create a list to store users information
2.Create a another list
3.Create the below Microsoft Flow:
4.Save & Test flow:
Thanks,
Echo Du
======================================
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.