TM F3/5 Factory reset without remote

Can someone remind me what's the procedure to reset the device with the power button and the up or down channel button please?
I accidentally changed the front display settings and the remote has become unresponsive, I do not have the PC with the serial port ready and I remember someone advised me in the past to use the power button and one of the channel keys on the unit, cant remember though the correct procedure.
Not sure, maybe I will try this although like I said remote is gone after changing the front display settings.
I remember anyway that a member of the sales team from TM instructed me on how to reset with the button on the receiver.
Maybe I will give them a call again.
Thanks for your input so far.