Dear Aaron,
Is the .bak file stored in Recovery Service Vault?
https://learn.microsoft.com/en-us/azure/backup/backup-sql-server-database-azure-vms
Or is this a VM you've created where you want to upload a on-premise .bak file?
Maybe one of these options will help you in that case.
https://learn.microsoft.com/en-us/azure/dms/tutorial-sql-server-to-azure-sql
Best regards
Theodor