combobox items and defaultselecteditems from different data tables

I have a combobox and in items i have cascading load data based on other combobox selection. then user saves data and it is saved to other table(Services).

The table data(Services) is loaded into gallery and this comobox sits within gallery so i want to load data what user saved into table Services.

On defaultselecteditems i simply type ThisItem.Work(Work is a lookup column in table Services to table Works) but this does not load the data that is saved in table Services.

THis is probably because Datasource for this comobox( now i see under properties it is called Items(Items)) is not Works?

How can i solve this?