All my Spanish friends would say: 'No te preocupes, no pasa nada.' It literally means, don't worry, nothing happens, it's like saying 'it's no big deal'.

That's mean: No te preocupes por eso.

You could also say: "No pasa nada" "No te apures" Nothing fancy but used everywhere.

Hola! You can say: ¡No te preocupes! ¡No hay problema!

There are some expressions to say that: - "No te preocupes" - "No hay problema" - "No hay porque preocuparse" the first one is the most commonly used.