How to remove a manual LT Threshold Input?

Hi,

when I got the FR 965 a couple of Weeks ago, I put in a manual LT Threshold HR.

Since the last update the LT Threshold Test is gone and in the linked Article  Improved Lactate Threshold Measurement Feature it says:

A manual reading can be input on your watch within your user profile under heart rate zones on the device. This will however turn off the auto-detect option and your device will ignore any future readings with this setting turned off.  

So, how do I get rid of this Value? There is no Delete Button.