You can add Queues to limit the rate for a specific IP or Interface , from queues simple queue add , you can limit the download/upload speed and apply that to a target , the target will be the IP of the user or you can apply that to the network by using slash notation , example :
If your network DHCP is 192.168.88.2-192.168.88.254 and you want to limit the speed with 2Mbps upload and 8Mbps download, then add this at the new terminal
/queue simple add target=192.168.88.0/24 max-limit=2M/8M limit-at=2M/8M