Locked file messages, notifications and visual overlays are only informative and do not actually lock a file. They are automatically created when someone opens a files, saves changed content and keeps the file open. Alternatively a user can manually create a Lock status. Automatically created Lock´s are automatically removed once the file is closed. Manually created Lock´s have to be manually removed.
In any case, any Space member can unlock a file.
If you want to find all locked files you can use the search filter function: