This tutorial will guide you through the process of migrating ejabberd from one host to another. Maybe it isn't needed to convert the Mnesia backup file, as mentioned here: Document how to change computer hostname.
Because ejabberd uses Mnesia as its internal database, and because this system stores the Erlang node name into the backup files, when you want to migrate from one host to another you have to 'convert' the backups from the old node name to the new one.