Your license is connected to the hardware ID of your computer. You are entitled to 3 resets per license.
Reset a license
In Air Manager 3.7 and up you can reset the license yourself. This counts for Air Manager and Air Player licenses.
Open Air Manager In the top menu go to Air Manager -> Orders In the orders window you will be able to reset your license(s)
How to find the correct hardware ID
If you are uncertain about the hardware ID, then you can find this in the log.txt. The log.txt can be found in the Air Manager or Air Player folder in the user folder of your system.
Microsoft Windows example:
To find the hardware ID from your Raspberry Pi, go to the Devices tab in Air Manager, right click on the Raspberry Pi and choose to download the log.
In the log.txt you will find a line displaying something similar as:
AMBase - HW id = ac291ef3r786b62063054a30df45efh9
AirPlayer: HW id = ac291ef3r786b62063054a30df45efh9
The hardware ID is displayed in the Orders window and can be used to distinguish the correct device.