Go to the web page (website / web interface) of your router / modem. You can access it using a web browser. You need to login there. To login, you need to know username and password.
When you have logged in:
Search for an option called "UPnP" or "Universal Plug and Play". Enable it. Search thoroughly for this option.
If you still cannot find it: search for an option called "port forwarding". It may be called differently, but it will look like this: a table where you can this enter port numbers and IP addresses.
You will need to add new entries to this table: Inbound/WAN TCP port 61357 needs to be forwarded to the LAN IP address of your computer (this usually starts with 192 or 10 - check your computer for its exact IP address). Save the configuration.
You should then be able to host.