How to turn off DFU mode on Mac

Press and hold the power button on the Mac until it shuts down.

Then press and release the power button to restart your Mac.

How to revive or restore Mac firmware - Apple Support

EDIT - I should probably add that if you actually started the process of the DFU revival then you should let it finish before you force the computer to shut down. There is likely a potential for a critical problem otherwise that might require a visit to Apple service.

If you mean how to completely disable DFU Mode so no one can trigger DFU Mode, then the answer is simple....you cannot disable access to DFU Mode since it is hardwired into the system firmware.

Otherwise, @D.I. Johnson has you covered.