Updating a Board Item with Zappier

Im trying to update a board item with Zappier and Im using the “Change Multiple Coloumns Value” action for this.
Unfortunately the board that im working with has a mirror coloumn and i dont want to loose the values thats already in this cell when updating it.
Currently my update action overides the entire cell and inserts the item.

Ideally i would like my zap to work as follows, but unfortunately it doesnt.

Could you please help?