It’s in the manual. See section 13.1
13.1 Input sockets and assignment
The input selection buttons select the source input signal to be routed to the power amplifier and the loudspeakers.
The NAC 202 has six DIN input sockets and two alternative pairs of RCA Phono sockets. The RCA Phono sockets can be assigned individually to the CD and AUX 2 input buttons in place of the DIN sockets.
Input assignment setup is accessed through the NAC
202 program mode. To switch into (or exit from) program mode press and hold the prog key on the remote handset (in preamplifier mode). Program mode is indicated by a flashing indicator on the front panel volume control.
note: If no function is operated within five minutes of entering program mode the NAC 202 will return to normal mode automatically.
Once in program mode press and hold the remote handset 1 button to select or de-select the RCA Phono socket input for CD, and the remote handset 6 button to select or de-select the RCA Phono socket input for AUX 2. The corresponding front panel input buttons can similarly be used to select or de-select the RCA Phono socket inputs. The appropriate input button indicator will flash three times on selection of the RCA Phono option and once on selection of the DIN option.
To exit from program mode press and hold the prog key on the remote until the volume indicator stops flashing.