Hi guys, so I have a one user ( he is Manager ) requesting to change his UPN because he still using the old domain (xxxx@oldDomain.com) to login to his computer and all his 168gb files are in OneDrive stored in cloud and connected to his 0365. Question, if I change his UPN to (xxxx@newDomain.com) in Active Directory can he still access all his onedrive files? Where do I start? Do i need to backup all the files locally before changing his UPN? Im really scared my boss gave me this task and I dont wanna screw up.

PS: Apologies my english is not good and im only 4months in my job as a jr It support level. Thank you