Media Library not showing the images

Hello!
I’m having a problem with the media library from wordpress.
I deleted earlier some images that had “size x size” (300 x 300) and others so i could clean a little since i had more images than i was actually using on the site.
Next thing i notice when i go to the library is that almost every image from the library is gone, but only when i check them on the media library, because the original files are on the host.
So what i’m asking is that if someone knows how can i “generate” new thumbnails for the files on my media library!

Best regards!