URGENT: Workflow not working - JoinFieldValue function plus 1 month addition

Hi,

I'm trying to update a date field: "Date 1" on Object: "SP" basis "Date 2" field on Object: "SR" with the help of JoinFieldValue function on a certain condition.

Desired Condition:

When [AB Picklist] = "N", then:

[Date 1] = [Date 2] + 1 Month

Currently applied following condition:

When [AB Picklist] = "N"

Action (Update Values post Wait for trigger When modified record saved):

[Date 1]= JoinFieldValue('<SR>', [<SRId>], '<Date 2_ITAG>')

i.e. currently, I've defined the condition & under Action: "Update Values"; I'm able to fetch the Date 2 value from the value stored in Date 1 field using JoinFieldValue function however can't figure out how to