How to capture the checkbox when a pop up screen is displayed and submitted?

Sorry to ask this question but I am now puzzled with this scenario.

In this screen below, I have a checkbox in the data table. Then once those are selected, I will click the button "Mass Change". A popup screen appears just like this one. User needs to input some new data first. When Submit button is clicked, it will submit the new data that applies to the employee that were selected.

When I am clicking the submit button, I got the new data but the selected checkbox is not.

Can you please enlighten me how to do it? Thanks a lot in advance.