I was making my Dark Elf Rogue Assassin and everything was going okay until I went to equipment and it won’t let me add the poisoner kit which I thought was strange since when I was first figuring the mechanics of the character builder it showed up fine for the thief class and I was just wondering if it was a bug or something on my side.

I can add it just fine. It's 'Poisoner's Kit,' not 'poisoner kit,' so try just putting 'poison' into the search bar and see if it shows up then.

I figure it out thank you!!