First it would be helpful to know what router modell you have.
Then you have to open the Router Menu which you normally do with a webbrowser ( like Internet Explorer, Mozilla Firefox, Chrome etc. ) by typing the IP Adress of the Router into the webbrowser and after that press enter. For example : http://fritz.box/ or http://192.168.178.1
The AVM Support writes this ( translated in english by Google Translator )
You can call the user interface either via http://fritz.box or the IP address of the FRITZ! Box (in the factory settings http://192.168.178.1). In addition, the FRITZ! Box is always accessible via the emergency IP http://169.254.1.1.
Click on "Internet" in the user interface of the FRITZ! Box.
On the Internet menu, click Shares.
Click the Port Shares tab.
Click the (Edit) button next to the (computer) name of the device for which the Exposed Host is to be set up. If no shares have been set up for the device yet:
Click "Add Device for Shares".
Select the (computer) name of the device in the "Device" drop-down list.
PS : As your router might be a different one as my AVM Fritzbox , just try to find the corresponding settings by google search.
I am sure you will find a lot of such information in the internet about your type of router.
And .... NEVER turn of Windows Defender ( Windows 10 ) !
Same rule for Antivirus and Windows Firewall for Windows 7 !