Boy: I'm sorry about that.
Girl: That's alright.
Boy: ?

In the above exchange, what is the normal response to acknowledge the girl's being understanding? Do we normally say 'thank you' or something else?
I agree with MrWordy. In fact, I can't think of anything appropritate to add.

If you're really desperate to keep the conversation going, you might say, "No hard feelings?" or something of that nature.

But better to change the subject.
There wouldn't normally be any need for the boy to say anything else.
Site Hint: Check out our list of pronunciation videos.
 Avangi's reply was promoted to an answer.
Thanks Mr Wordy and Avangi. It was very helpful.