The following terminals at your RX1 have wires connected:
N
L
2 -Com
3- On
If so, set the Tado Extension box to the potential free setting and move the wires over including the loop as follows:
The wires in RX1 N go to Tado N
The wires RX1 L go to Tado L
The wire in RX1 2-Com goes to Tado 1-COM
The wire in RX1 3-On goes to Tado 4 - NO
EDIT
I assume that you have a combi boiler providing instantaneous hot water, and not a hot water cylinder. If you do have a hot water cylinder and want timed control of the hot water then you are installing the Tado in the wrong place, not all the wires you need are present. If you have a combi, carry on as above.
I don't know what type of thermostat is presently working in conjunction with your RX1, but if it isn't a programmable thermostat and there is a timeswitch elsewhere providing on / off time control for the heating (eg on the boiler) then that will need to be set to be permanently 'on' 24/7.