If you didn't delete Studio's backup, they should be in your Sims 4 Studio's folder at Documents. If you did delete the backups then there's no way to get the thumbnails back other than downloading again the CC.
Last Edit: Apr 30, 2019 18:01:22 GMT -5 by Mathcope
Please do not PM me to help you with your creating problems. You can post in the Creators Help so everyone can see the problem and solution.
I made this BIG mistake too, and even went to the back up for the remove thumbnails fix but nothing I could do would restore the original thumbnails. I REGRET deleting them because now many of them are unrecognizable and I have to memorize their location instead of recognizing a thumbnail. I think there should be a stronger warning about this
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