When a page or post is being edited by one user and another tries to open and edit the same, WordPress by default shows a message “user is currently editing” on a page/post listing screen.
If you still go ahead and click the “Edit” link, you will get a popup/alert on the edit page/post screen like below:

WordPress provides this so that users don’t overwrite each other’s content accidentally. What if you want to disable this feature? Recently similar question was asked on WordPress support forums and this article is an inspiration from that support ticket.
You can disable this default behaviour with a single line of code. The wp_check_post_lock_window
filter hook is responsible for this.
add_filter( 'wp_check_post_lock_window', '__return_false' );
You can add this at the end of functions.php file of your theme OR if you are using a plugin like Code Snippets then you can add this snippet from WordPress dashboard also.