iPhone 11 Pro Max synced to wrong apple account

In setting up my husband’s new iPhone 11 Pro Max, instructions said to go online to start the setup. I used my iPad (with my Apple ID) to start the process. Before I realized what was going on - I had downloaded my iCloud backup to his new phone instead of his iCloud backup. I’ve read all the responses but none of them seem to help with this situation. I want my iCloud backup deleted from his phone and I want to download his iCloud backup to his phone. Anyone know how to do this?