change state in checked of a checkbox in another thread

change state in checked of a checkbox in another thread

hi there i search but i don't find any answer. I have a thread which has a
form whith some checkbox whith default state unchecked and disable. i need
to change state at some of that checkbox if i terminate some action in the
main thread . for example when in the main thread i finish a method i need
check the checkbox in the secondary thread. thx
i start my thread from the main thread whith:
Thread t = new Thread(new ThreadStart(waitformstart));
t.Start();
The second thread is only a windows form whith a gif and 4 checkbox thx so
much