If the backup is a text file,

badlop — Wed, 24 May 2017 09:41:15 +0000

If the backup is a text file, you can simply edit it before importing in the new server.

If the backup is some binary file that you can't edit, then you can:
1. import/restore/recover the old backup in the new server
2. Dump the database to a text file
3. Edit that text file, changing the account domains as you want. Make sure you respect the file syntax.
4. In ejabberd, delete the database contents, as they are old.
5. Then load the edited text file.

For 1, 2, 4 and 5 you can use ejabberdctl commands.

ejabberd - Comments for "restore backup under new host name"

If the backup is a text file,