You do not conventionally use the frequency as an on-off switch. That is why you have a run and a stop button on the keypad.
You can change the behaviour of the potentiometer (to turn it into a stop switch) with parameters 0.06 and 0.07.
When you install the switch on the control circuit, you need to set the parameter for the computer to obey that switch (i.e. one of the multifunctional input terminals, see parameters F.2.13-2.16).
Any industrial momentary push switch will work with the VFD. A 22mm panel hole is a very standard item. The challenge may be finding the place (and mangled English description) in the manual where you tell the computer if it is to use momentary or maintened switching. You will know if you have it wrong if you have to hold down the button to make it work.
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It may be wise to keep all your queries in one thread/topic rather than start a new one with each question. Perhaps ask a moderator to merge this one with the previous one.