How to reset app's badge?

It was 20 unread notifications of Tweetbot on my iPhone and some on other apps before restore. Well, I did the restore from backup. Now if I read all the notifications and get, say, new mention notification in Tweetbot, it show not "1" on the badge but "21". And then I read it, I see no badge... And if I get one more tweetbot notification, it shows "22", etc. on the badge.

I'm just wondering if I could safely reset that badge without losing all my data. How do I do that?