How to configure in mqtt

i am using your development kit which consists of raspberry pi and lora wan 1032 i have read that i have to update the mqtt configuration in chirpstack-gateway-bridge package i dont know how to do this can anyone helpme with this??

2)and i running this command on home dieectory sudo journalctl -u chirpstack-gateway-bridge -f -n 50 but that does not seems to be working it shows command not path how can i rectify this

thanks and regards