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 Return. 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 Return 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 Return, 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 return field. After you have chosen your one-way travel date, click Confirm at the bottom of the screen.