If you want to remove the server extension after you have completed a migration, your server administrator needs to go into the Programs and features of each of your web front-end servers, and uninstall the ShareGate Migrate extension.
How-to
Open the Control Panel.
Under Programs, select Uninstall a program.
From the program list, locate and select Sharegate Extension.
Click Uninstall located in the top ribbon.
Follow the prompts in the dialogues to complete the uninstallation.