Hi,
An optional action in a process is used to add information to your ticket and didn't change the process status. Optional action can be set directly in state ( status'sproperties) or by expanding it on process ( linked to status)
In your case, You should link your action from your status " in progress" to " waiting..." status: you do this by dragging and dropping a manual action called add affectation.
Your process should be deactivated before making this change.
I hope that is helpful
Regards