(Firstly, I don't know if "parent" module is correct way of describing this?)

I have a custom module (Jobs) that has multiple Deals (Tenders) associated with each Job. When the "job status" field (pick list) is updated on the Job module I want it to to cycle through the Tenders associated with the job and update the Tender's "stage" field (pipeline) to a new status. 

I have tried creating an action and using a workflow to do this but the workflow fails because it "can't find the record". 

Any guidance would be very much appreciated.