Go to Configure > Services, Locate and double-click the service in the Services list.
The Edit Service Item screen displays. In the Custom Screen field, use the list selector button
Back in the Edit Service Item window, select the appropriate popup behaviour for the custom screen:
Popup disabled - You can complete the custom screen but it never popup for the user.
Popup when planned - When the service item is first charted it will prompt the user to fill in the custom screen.
Popup when completed - The custom screen will prompt the user to fill in the custom screen when you mark the service as completed.
You can also do the same from Configure > Custom Screens:
Highlight the custom screen and click the Set Services button at the bottom of the screen:
The right-hand section will show all the services that custom screen is attached to and whether the popup is disabled (D), set to popup when the service is planned (P) or to popup when the service is completed (C)
You can highlight the service you want to add it to on the left hand side and click on the >> button to move it to the right and then tick the popup option you need.
You can repeat this for each service you want to add on.
Once you've configured the custom screen services, select OK to save or Cancel to discard.