The dongle you are talking about is a necessary component for your software because it has been designed to run with the dongle attached to the computer. In some cases this device acts as an activation key for increased security. It means that nobody will ever copy the licence key. Older dongles were connected to the serial port of the computer but as the technology evolved, the connection is made through protected USB.
In other words, you will not be able to install and use the software on the computers you specify unless you plug the required dongle. If you lost your dongle, please contact the company which developed the software.