you need a gateway bridge for each region talking to the correct mqtt topic for the region as brocaar is alluding to. this is setup with the correct topics already in the chirpstack/configuration/regional_config.* file(s) which are picked up via the chirpstack.toml for the regions you have enabled. double check you have the correct topics in the config files
an example to do it over docker is here Multi-region with V4 and Docker Compose - #7 by Tom_Z otherwise you’ll have to start and set a gateway bridge for each region with systemd or something and make sure the set the ports don’t clash.