Woohyun:

A: Hey, why are you sad?
B: Because my grandmother had passed away.
A: Aha! so you were brokenhearted when we had a party yesterday night.
B: Yes.
A: Don't worry, my friend! I will cheer you up.
B: How?
A: We will go somewhere. See you tomorrow!
B: Bye.

Correct:

A: Hey, why are you sad?
B: Because my grandmother had passed away.
A: Aha! so you were brokenhearted when we had a party yesterday night.
B: Yes.
A: Don't worry, my friend! I will cheer you up.
B: How?
A: We will go somewhere. See you tomorrow!
B: Bye.

Hello Woohyun! Thank you for submitting your homework on Talk Fun. Well, the idioms are used well and your sentences are constructed properly. It's a simple dialogue about friendship. I  would like to suggest that it would be better if you write names of your characters in your dialogue to emphasize persons and so that it will be a  more realistic conversation. Mostly, you did a good job.  See you again in our class.