Channel mappings may differ on custom f3 boards, however the default F4 and clone boards like below should be the same.
To connect this FC to a Flysky receiver in PWM mode the channel mapping is as follows:
RX FC
CH1 ---> CH2
CH2 ---> CH8
CH3 ---> CH1
CH4 ---> CH7
CH5 ---> CH4
CH6 ---> CH3