Before uninstalling ExtendSim, be sure to revoke the license using the Help > Revoke License Activation command (or the Help > Deactivate ExtendSim command if prior to 10.0.5).
After the license has been revoked, use the Windows Settings > Apps and Features to uninstall ExtendSim.
Finally, delete the two folders: Documents\ExtendSim and Program Files\ExtendSim. (The remaining contents of these two folders were created after installation. The uninstaller couldn't remove those files because it didn't know about them.)