There is not any interface or webpage allowing you to manage or control your activation count for Guitar Pro 7.
It it your responsibility to respect the Guitar Pro Software End User License Agreement, that states among others that "the License acquired hereunder may be used to activate the software as many times as desired, within the limit of up to 5 computers at the same time. Beyond these 5 computers, the User shall first uninstall the software before installing it on a new computer.
In any event, the use of the License on multiple computers is limited to the different computers of the User, and their family environment (same household) in the case of private use.
To remove your license from your computer you can go to the :
Help > About Guitar Pro 7 menu (Windows)
Guitar Pro 7 >About Guitar Pro 7 menu (macOS)
And select "Remove license".