Click the "Connect" button on the left, and wait for the "Port mappings" list at the top to be fully populated and enabled (if nothing appears but the box turns a white colour, it's enabled but you don't have any ports open).
Click on the "Create" button on the right hand side

A dialog like this should then appear:

You want to enter a description at the top (I use "The Sims" as mine), and then click "Add" on the left.

Change the "External Port" value to 37564, and the "Internal Port" value to 37564 also. Then, do the same again, but change "Protocol" to UDP.

Click "Save". The dialog will then disappear; you must then highlight the description you entered earlier, and click "Use".
Check that the "Port mappings" list at the top of the window has your two ports entered, and then you can close the window safely.