Automation - how to target a triggercard custom field value

[Heather Lueck - Client Care Team]

Using Cascade Automation feature.

We have a trello card for each client (with the name of the card being the clients name) 

We also have a  "Master Possession Date" card we use as a tracker. I've managed to automate with a checklist item that populates every time a Possession custom field is set, as follows:

when custom fields "Possession" are completed, find a card titled "COF and POSSESSIONS Master Checklist" in list "Admin/Misc" on board "Client Care Team", and add item "{triggercardname}" to checklist "*Automated Possessions Added"

this works great, and creates the checklist item with the name of the triggercard - on the Master "Automated" checklist - but I cannot figure out the next part - which would be setting the due date on the created checklist item - to the same date that was filled in on the triggercard custom field. 

I know this is the root trigger for this next step: "set the item due on the date in custom field "Possession" - but its trying to pull this Possession date from the Master card - not from the original trigger card. 

Ive also tried to add a new second rule to accompany like this: when an item is added to checklist "*Automated Possessions Added" by anyone, lookup a card titled "{checklistitemname}", and set the item due on the date in custom field "Possession" - but this doesnt work. Still trying to pull the Possession date from the Master card - instead of the client card. 

Does someone know the proper trigger to target a custom field date from the triggercard? HELP