First make sure the toolkit is installed with VI Package Manager (VIPM) running with administrative rights.

Once installed, open the LabVIEW menu option Help/Activate Add-Ons... and select the MQTT Toolkit

NOTE. This also works for expired trial versions.

Press Activate and choose desired activation method (default is automatically over internet)

Enter the License details (LicenseID and Password) in the corresponding fields

Finally press Activate to activate the toolkit