Where is my border?

i know this is extremely late but a couple months ago during that event that had to do with Warwick and Lux and one other champion i forget the name of it though i used the stuff we got from the missions to get a shiny yellow border for the loading screen, but i have no idea where it is or how i equip it or if it was just allowed during the event. i’m relatively new to league still and i’m still trying to find out all the stuff i don’t know so if anyone could help me out here that’d be great.

thanks!