How to "Unlock any signatures that have been manually set against activities after the identified breakthrough activity."

In article [https://baronbiosys.com/xerts-magic-setting/](Xert’s Magic Setting – Signature Decay)
They say:

  1. Unlock any signatures that have been manually set against activities after the identified breakthrough

activity.
and

  1. Save/Lock the activity with the identified breakthrough

How one (un)lock signatures? And what (un)lock means?

Related with the info you need – What is Advanced MPA? – Xert (baronbiosys.com)