To enter or change your backup address, go directly to your Microsoft 365 account at the following address: https://mysignins.microsoft.com/security-info

Adding a backup address :  

1. Click on Add a connection method
2. Select Email from the drop-down list
3. Click on Add
4. Enter a personal backup e-mail address (this will be used to recover your business account in the event of a problem).
5. Click on Next
6. Enter the verification code received on the backup personal e-mail address 
7. Click on Next

Your backup address is now configured

Modifying a backup address :

1. Click on Change next to your backup e-mail address
2. Replace the existing address with the new address you want
3. Press Next 
4. Enter the verification code received for the new address 
5. Press Next

Your new backup address is now configured