Regarding transmitting and receiving in two different frequencies

hi
I am looking to make a transceiver work such that it receives the data
and then transmits its own and other nodes data that it got.
I am new to python and gnuradio and so I have been modifying the
benchmark_tx and rx.py, so far to do my project, Since I have to make
the receiver to work first and then the sender, I added the
transmitter code to the def_rxcallback function and it worked
correctly.
But I am not able to transmit and receive in two different
frequencies, though I see come expert options in the help window of
the program such “–tx-freq” and “–rx-freq”.
Can anyone help me in setting up the option such that I can set two
different frequencies for both transmission and reception?

thank you