Turn off the Tamper Protection Feature in the ThreatLocker Portal

Disable Tamper Protection | ThreatLocker Help Center (kb.help) 

Click on the ThreatLocker icon in the tray. Select 'Quit'.

Drag the ThreatLocker App icon from the Applications folder into the bin.  

You will receive a message informing you that the ThreatLocker app is hosting system extensions. Click 'Continue' on the popup.

If prompted, input your username and password and click 'OK'.

You need to ensure that all baseline remnants have been removed.

Open Terminal by clicking the icon located at the bottom of the screen.

Input: sudo defaults read com.threatlocker.app.agent  

This will check to see if the baseline is present. This can also be useful if you wanted to check to see if the baseline is complete without logging into the ThreatLocker Portal.

Run the following Terminal command: 

open /Applications/ThreatLocker.app --args -uninstall 

This will delete the baseline. This is especially important if you are removing the ThreatLocker App to reinstall it.  

Lastly, you will go into the portal under the Computers tab, select the machine, and select the delete button.