If you want to forward your subdomain of your domain to a specific webpage of your domain then you can do it by following the below mentioned steps:

1) Open the web server IIS of your server.
2) Right click on appropriate subdomain name.
3) Click on Properties.
4) Click on Home Directory tab.
5) Select the A redirection to a URL option
6) Enter the appropriate URL of the webpage in the textbox at which you want to forward your subdomain..
7) Click on the exact URL entered above checkbox.
8) Click on Apply button to apply the changes.