When you run the Agent installer (.msi) file, Windows initiates installer processes (msiexec.exe). Manually cancelling an Agent installation requires canceling these processes.
First, check the status of the installer process:
Confirm that msiexec.exe is listed among command line processes.
To cancel the process, select msiexec.exe in the process list, and click the End task button. Ensure that you cancel all instances of the msiexec.exe process.