Hi Luis, I'm waiting on a similar answer to this myself with an open ticket in support. I have a Job Scheduling form and each Job receives a sequential and unique "Job number"  assigned in a field entry (easily done in formidable). Then I created a "Job status" field entry with 4 drop-down box choices.

Unassigned
Assigned
Partially Completed 
Completed

Now that the entry is created I need the "User_ID" assigned to do the job to be able to update the "Job Status" field in the original entry via a secondary form so that entries into one form update another. But it needs to look up the "User_ID" and the assigned unique "Job number" and then update the field. I tried using some examples shown in tutorial for adding code to functions.php but this updated all Entries assigned to "User_ID" not specific ones by "Job number"I also used the edit-specific fields feature (adding it to a calendar view) to edit the original entry and assign it to the user, but it dropped other fields in the entry after updating the field specified.