Garage Door Opener Spring Compression Tool

The rented house I am living in has a broken garage door opener, and the garage door does not have a handle on the outside for opening it manually. The landlord also would not replace the garage door opener since it isn't on the lease. As such, I purchased my own garage door opener. As I plan to take my garage door opener with me when I move out, I will need to uninstall mine, and reinstall his broken one. Part of the installation process is using this little spring tensioner for the belt drive.