1
If the app is on your taskbar, right click the app, is there an option to 'Unpin from Taskbar' on the resulting menu?
2
If not, open the Settings App.
Go to Personalization - Taskbar.
Check in each section on that settings window to see if you can find the app, if so, are you able to remove the app from there.
3
If not, open File Explorer, then paste this into the Address Bar and press Enter.
%AppData%\Microsoft\Internet Explorer\Quick Launch\User Pinned\TaskBar
In the resulting folder, do you find that ap and if so, can you delete the app from there.