I am not fully sure what you mean, but here u go
It is not possible to unlink an account when it is linked(it is possible) and kabam cannot be bothered doing so.
If you mean changing the email on the steam account itself there is very simple instructions here https://support.steampowered.com/kb_...3176-RTKC-3810
Contact steam/kabam support depending on which type of issue above it is^^ they might be able to help you better