How to set a field equal to another field in SugarBPM

I'm trying to set up a SugarBPM process that will be integrated with a Customer Journey. The first task in the Customer Journey calls for assigning an Engineer to an Opportunity. The several subsequent tasks have to be assigned to the Engineer above. I'm trying to automate this, so that when the first task is completed and an Engineer is assigned to an Opportunity, the Engineer will be automatically set as the Assigned-To user of subsequent tasks. In order to do this, I'd need to set the Assigned-To user of a Task equal to the Assigned Engineer of a related Opportunity. But I don't see an option in SugarBPM to set a field equal to the value of a different field. Is there really no way to do this in BPM, or am I missing something? If this is impossible in BPM, then I'll have to set up a custom logic hook.