Dead in Thay - Add On option not existent?

1518568904

Edited 1518568944
Hello, I purchased the Dead in Thay add-on individually instead of the entire Yawning Portal package. In the description before I bought it there was instructions on how to add it to an existing game by going to Game Details -> Game Settings and then going to a game add-ons dropdown. Only this mythical dropdown is nowhere to be found in my game's setting page. Am I just blind, or was there an update or something that changed how add-ons are added to a game? This is particularly frustrating, as I bought Dead in Thay specifically to add its monsters to a custom campaign, and I can't seem to access the monsters from it at all.
1518569705

Edited 1518571360
Nevermind, I found it. The add-on dropdown is now directly on the game details page, no longer in Game Settings. If possible, perhaps fix the description of big ticket Marketplace add-ons (official WotC stuff) to describe the updated method for using add-ons. Would cut down on confusion.