Can I use a 9 Volt 1 Amp power adaptor in place of a 5 volt 1.2 Amp adaptor?

No, the voltage of the replacement adapter must always be IDENTICAL to the original adapter and the current of the replacement adapter must be the same or larger than the original adapter.

Trying to use a 9 Volt adapter to replace a 5 Volt adapter will almost certainly completely destroy the device the moment you plug it in.

You did not say whether the adapters provided AC or DC or the polarity if DC. Either way both the replacement adapter and the original adapter must be IDENTICAL in this respect.