Hey guys, I have worked out how to fix this error
First of all, the icon that shows up on your task bar is basically a shortcut (If you right click on it, you can see for example if it shows the css icon (Will work with all other icons too), it will have Counter Strike Source above the "Pin this program to the taskbar"). It uses the icon from the shortcut that is in that menu so all you have to do is delete it from the desktop and then it should go back to your normal Steam icon. To get the icon back onto your desktop, go onto your steam games tab and then right click on the game of the icon that you deleted and then click "Create Desktop Shortcut"
The problem should be fixed
I hope this helps you