You can refresh the subform on the navigation toolbar when some subform element has the focus.
When a list box or combo box is foussed, you can use the second refresh button to refresh the list of the selected element.
Instead of the navigation toolbar, you can attach a navigation control to the subform. Use the form navigator to make sure that it belongs to the right subform.
Instead of any of these toolbars, you can attach a push button with action "Refresh form".
It might be possible to create a refresh button for a list/combo box by using an URL button with the right dispatch URL.
Dozends of refresh macros have been written over the years.
This is my version of a universal refresh macro triggered by a form event:
https://forum.openoffice.org/en/forum/v ... 21&t=88831 to refresh any (group of) forms/combos/lists after the current record has been removed/updated/inserted