The ability to use iMessage Apps was one of the cooler new features added to iOS 10, but with so many developers adding their own little iMessage apps to their main apps, you may find your Messages app drawer quickly becoming inundated with new icons. Fortunately, it’s not difficult to remove or reorganize your iMessage Apps, or prevent new ones from automatically showing up when one of your existing iOS apps gains iMessage App support in an update.

Removing and reorganizing iMessage Apps is done in much the same way as normal apps on your home screen — just bring up the app drawer in iMessage by tapping on the app symbol to the left of the text entry field, and then tap-and-hold on any one of the apps until they all start jiggling.
From there, you can drag them around to reorganize them, even between pages, or tap the “X” in the top right corner to remove the app entirely. Removing a dedicated iMessage App like a sticker pack from here will remove it entirely from your iPhone, iPad, or iPod touch; removing the iMessage App version of a standalone app, on the other hand, will only hide the iMessage App extension, leaving the main app untouched.
Tapping on the Store button in the top left corner of the iMessage app drawer will take you to the App Store for iMessage, where you can find and install additional apps that work with iMessage.
There’s also a Manage tab on the top right that will take you to an alphabetical list of all of your iMessage Apps. Toggling any app “off” from here removes it from your iMessage Apps in the same way as removing it from the main app drawer — dedicated iMessage Apps will disappear from the list entirely, while standalone apps which provide iMessage App extensions will remain in the list in an “off” state.