Hi, I have a workflow where I want to set a value for a custom record, why can't i access a custom record field?

Assuming the workflow is running on that custom record as the record type and you haven't locked down the permissions in the field or the custom record somehow, you should be able to do this.

Yea you need to setup your workflow to run on the custom record you want to manipulate in the overall workflow configuration Then the fields for that custom record should be present to manipulate