How to portforward a minecraft server?

I try to make a port and all it says is " Conflicting Port Forwarding Rules:The Minecraft service conflict with an existing port forwarding rule offering Destination Ports 25565 service." What do i do?

You can either change the port (25564 for example) or find the conflicting rule and, if it's not an important port, disable it (temporarily if it's vital) while your Minecraft server is running if your router allows that. If not, use another port for your Minecraft server.

The port will only be open while your server is running/online, so it shouldn't be a security risk as long as you're careful in choosing a port for your server.