Hmmmm let say now. at first, they choose machine 2. Machine 2 now is “not available” status.
The remaining machine are 1, 3. If they want to change the machine they can only choose either 1 or 3. No machine 2 in the list. So, if they accidently chose 1, cannot back to 2 unless click Done (at choice component ) and cancel the entire edit form .