Please launch your browser and enter http://dlinkrouter.local or http://192.168.0.1 into the address bar. Then login and follow the steps below:
Step 1: Click Connected Clients from the Home Tab:


  
Step 2: Click the Pencil Icon next to your client you’d like to adjust:


 
Step 3: Click Reserve IP to Enable, and fill in the reserved IP address, then click Save.