Items in Matrix can be locked by setting dedicated lock labels.
In case an item has been locked it cannot be changed through the user interface until it is unlocked by someone with the rights to do so.
To create a lock label:
- go to the Labels project setting and create a normal OR label
- go to the Locks project setting and create a new lock
- select the label
- define the users who can reset the lock
In the following video (direct link here), see how to lock some specific item to block others to make changes: