The complete case is this:

We are already tracking one picklist field history with the functionality that Zoho provides, but now I want to track another picklist field history with a workaround that came across my mind by creating a subform and writing a code in order to create a new entry within the subform whenever a picklist value is changed to that field. 

So the workflow would be:

Client Activity has been modified >>> Reason text field becomes mandatory >>> User provides mandatory information >>> Workflow is being triggered >>> Function creates new row within the subform with Client Activity status in one field and Reason in another field.

That way we could report on the history related to that field.

Please help me with this coding as I have only basic knowledge of Deluge and I'm not sure how complicated would this code be.