Hahaha both is correct but pure Hindi is second one.first one is local language

चिंता मत करो इस बारे में

The first sentence is extremely informal and should be used only with very close friends. With anyone else, it sounds offensive.

भेजा मत खा-- It's a very informal way of saying "Don't irritate/disturb me". (इसके बारे में) चिंता मत करो-- It means "Don't think much/get annoyed/worried." चिंता means keep thinking about something and get worried. The second one will be good to use in this case.