Hi travis, if you uninstalled IDM, restart the computer so that the file can unload, then delete it.
Otherwise, download Autouns:
https://docs.microsoft.com/en-us/sysinternals/downloads/autoruns
Extract Autoruns64 and run as administrator. In the Quick Filter box enter: IDMShellExt64
Right click any found entries and Delete
Restart the computer and delete IDMShellExt64.dll