While Rebirth isn’t a feature in Diablo 4 yet, it may be potentially added in the future, according to Pezradar.
What’s Rebirth?
Rebirth is only available in Diablo 3.
If you wish to participate in a Season but do not want to create a new character, the Rebirth option lets you transfer an existing character to the current Season.
After selecting one of your characters, you can use the Rebirth button, which will convert them into a Seasonal hero, revert it to Level 1, and mail the items and stash contents to your non-seasonal mailbox.
