In Sitecore, you can lock the current version of the item you are working on to prevent other users from editing the same item at the same time. If the item that you want to edit is already locked, you cannot edit it, you can only view it. When you have finished editing the item, you must unlock the item to make it available to other users again.
Sometimes we need to force the unlock because for example the person who locked the item is not present.
In this case, this powershell script could be useful :