Unignore Bluetooth Device with iPhone16

I have read many comments here about this issue and people who keep saying place the Bluetooth device in pair mode are ignoring what the problem is. In all these case the Bluetooth device IS is pair mode but the iPhone will not recognize that it even exists - it ignores it totally, there is no indication on the iPhone that the Bluetooth device even exists while it is in pair mode.

So again, how do you "un-ignore" a Bluetooth device on the iPhone?