The easiest way is to travel to the marketplace map for your starter kit.
There you spawn at Beach 3 and go into the building at one of the Vault's that hang there.
Use the radial menu to select Reward Menu, then the store window will open.
Here you can click on Starter Kits and select the starter kit, by clicking on Purchase
unten rechts hast du es „gekauft“ und findest es jetzt im Inventar der Vault, wo du es rausnehmen und benutzten kannst.

Have fun and success with it.