If the logbook is already completed by the user, the information will still be there as long as the logbook is in use.
When following the below steps, the logbook won't be visible at all in user's profile:
Going to Settings then click Logbook.
Select the relevant one then deselect the In use button.
📌Note: After putting it in use again, even if it has amendments or not, the previous information that was inputted within the logbook by the user will still be there but now they will have the additional fields added to the logbook and they will need to complete them or they can leave it like that. If you change the logbook, everyone who is assigned to it and have it completed will get the additional fields.