How to Using Dropdown - which data source is Data Object

i have created an data object also with the data services etc. used H2 database in flowable trail version.

now i want to create a dropdown list (select - single) in a form, and the data source is one field of the data object. i dont know how to config it.

In my case, i want to get “summary” field in data object, and let user select it, then flow to next step.

here is what the datatable looks like, as an example, i want user to select in “TestProject”, “aaaaaaaa”, etc.