This icon appears on the left side of Lost Ark Gold your screen.
Once you click on the box after which you'll see what you have in your Founder's Pack, press on Claim.
Open up your Inventory.
Just right click on Founder's Pack.
Choose Open.
The contents of the pack will be incorporated into your account, including that Lawmaker skin.
The Northern Lawmaker skin is made from cheap Lost Ark Gold four distinct parts, which means you'll have to have all the parts to fully equip the skin.