Upstairs, fixed IP is assigned to the specified MAC address, not interfaces. For example, my router has 24 interfaces. I think the IP address assigned to the network cable of interface 10 is 192.168.1.10, and the IP address assigned to the network cable of interface 11 is 192.168.1.11, and so on. How to set this way, because the online client is a laptop, which is always changing, and there is no way to assign IP address according to Mac
The "port" of the router/switch is irrelevant, ultimately it is the CLIENT MAC-address that determines which IP it will receive.
Using the Mikrotik-DHCP service, you cannot "force" (to my knowledge) a device to receive 192.168.1.10 when plugged in Port10 or 192.168.1.17 when plugged in Port17 because I think this is what you are looking for?
"the online client is laptop, which is always changing" =>
Is this a MAC-book or Android device ? Check if there is a setting "Privacy" on the network-setting that makes RANDOM MAC-ADDRESSES making it indeed impossible to provide a specific IP to certain MAC.
Android phone on their Wifi have the same setting, iOS devices also.
To be honest, this is a wild guess from my part as your question/requirement is almost not understandable!