Permanent IP for Xiaomi Gateway

Hi, I’m using OH 2.4 on RPI 3b+
One question that sometime make me crazy.
Xiaomi Gateway change his IP and I need to locate it again in my Internet panel.

How can I do it permanet ?
Thank you.

I don’t have one so my advice might not be correct.

I assume that per default it runs as a DHCP client. This means the DHCP server ( that is normally your router ) provides a free IP address to your Xiaomi gateway.
Either the Xiaomi gateway offers the possiblity to enter a fixed IP address or you need to get it’s MAC address and enter it in your routers UI to always send the same ( fixed ) IP address to the gateway.
It depends on your routers UI if that is possible. If that is not possible the only alternative would be to use a different computer and make it DHCP server instead of your router.