2 were created before we had our domain name verified

These were assigned a abc.zoho.com address

2 were created after we had our domain name verified

These were assigned a abcd.ourdomain.com address

We need to be able to forward mail from our current ISP until we decide if we want to use Zoho Mail full time

The 2 accounts that had abc.zoho.com we could forward to from the current ISP.

How do we forward to the 2 accounts that do not have a abc.zoho.com account?

Thanks in advance