ok so at last i got it
here are the steps to connect the Behringer FCB1010 to Randall RM100 for those of you who can't manage to get the channel switching
1. Open the chassis find the DIP switch near the midi in and thru board, put the 4 switch to off position (channel 16) , there are another switch located near the MIDI IN slot (2 switch) check if its on the ON position, it must be ON (not necessarily)
update
The switches all down would be midi channel 16. The two other switches to the side are used to turn phantom power on and off when using a 7 pin midi cable.
(response from Randall USMC, so the last 2 switch is for the 7 pin midi cable)
2. Reset the Behringer pedal to factory setting by pressing button 6 and 1 while powering the pedal,just hold it, there will be digit 9 counting down to 0, and youre back to factory mode
3. the factory mode usually already in channel 16 at least mine do, so if you want to check the midi channel just got to global configuration by holding the down button while powering the pedal, press up untill the green LED got into the midi function, press the pedal 1 and press up to the midi channel (green light will guide you) check the value it should be 16, pressing and holding down button will get you to the preset mode.
4. go to the preset 1, for some reason my pedal 1 dont want to be assign to channel 1 so i start from 2, press the button 2 till the red light is on, go to the amp and press and hold the channel selection button while it is on channel 1 (if you want to assign pedal 2 to channel 1), just do the same for all the channel
this is the way that i do it hope it helps