Custom link to different site?

Hi, I’m trying to use a custom link (through the advanced custom fields route), it’s doing what it’s supposed to do, however I want to link to different sites! The links at the moment come out as “www.mysite.com/www.desiredlink.com” which obviously doesn’t work. am I missing something here, because I can’t figure this one out.

Link: http://www.rcvys.org.uk/wordpress/home-2/

Thank you!

https://wordpress.org/plugins/advanced-post-slider/