On your 1660ti you have 3 output. 1 dvi, 1 DisplayPort, 1 hdmi. On your photo, you use the dvi port with , i think, a dvi cable to plug your first display. Rigth ? so now you can use a hdmi câble or a DisplayPort cable to plug your second display if this one have a hdmi entries or a a DisplayPort entrie. If it have only a dvi entrie, then use a dvi-hdmi cable 
Hello all, I have a dual display and purchased a Dell XPS with a GeForce GTX 1660 Ti graphics card. What would I need to be able to use my second display? I have attached an image of my card. Thank you![IMAGE]
Display Adapter for GeForce GTX 1660 Ti needed