To search for one-way flights on Skyscanner, follow these steps:

On the desktop website, click on the date in the Depart field. At the top left of the date selector, there's a drop-down field that states Roundtrip. Click on this drop-down field and then choose the One-way option. 

On the mobile website, select the Choose dates field. On the next screen, you will see an option from the drop-down field to switch from Roundtrip to One-way.

On the mobile app, select the Flights option when opening the app. At the top of the screen, there are options for Roundtrip, One-way or Multi-city. Select the One-way option. There is also an option to switch to One-way within the date selector, by clicking the X symbol in the roundtrip field. After you have chosen your one-way travel date, click Confirm at the bottom of the screen.