Thanks for reaching out and welcome to the Community
Unfortunately at the moment there isn't an option to select multiple playlists and delete them. It seems however that other users also requested this to be changed and posted this idea. We recommend that you +VOTE it to show your support. We'll share any updates on the matter there, as soon as there are any, so it's worthwhile that you also subscribe.
In the meantime you can reach out to out Customer Support team here. They have the option to reset your music library to a previous point in time.
Hope this helps. Keep us posted on how it goes.
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