TB is having a lot of problems working with YT backend server functions at the moment. The last time I tried a bulk edit of any kind it was not working. Hopefully, they can get this fixed soon. As far as bulk replacing entire descriptions, I doubt that it can do that, UNLESS all of your descriptions are identical. Honestly, I cannot see how having identical descriptions on every video would be remotely beneficial. I have sections on every video that are the same, such as a disclaimer, that occasionally I need to update and modify, but having the identical description on every single video seems that it would be detrimental to your channel.