I'm using the PiGPIO library to receive a waveform but I don't see a way to make sure the RF frequency is correctly set. I'm using the class rx() which is supposed to read a signal transmitted on 433 MHz, but I'd like to change this value. I've search in pigpio.py but couldn't find it.
pigpio doesn't read the 433 MHz signal. The signal is picked up by the wireless receiver hardware which passes on 1s and 0s to the Pi. You get a 1 while the 433 MHz carrier is present and a 0 otherwise.
The actual radio frequency is irrelevant to pigpio, that side of things is automatically handled by the transmitter/receiver pair.