Macbook Pro App icons changed

I have a 2017 Macbook Pro 15-inch with a 2.8 GHz processor. Recently, the icons for some of my apps started to change without me doing so. The regular icon no longer is shown and now shows a grey rectangle with an "A" made from a pencil, brush, and ruler. It started with one app, and now it is five. I have checked for updates for the apps, and some have updated, but they have remained unchanged. The one app was a game, League of Legends. When it first started, I would uninstall it from the computer and re-install and it would sometimes fix the problem, but it would change again. When I would put the game on the dock, it changes the app eventually to the "A" and grey rectangle. Currently system Preferences is changed on the dock. Safari, Keynote, Microsoft Excel, and Microsoft PowerPoint are changed in the app menu.

Can someone please offer any advice on how to change the icons back to normal?