Hi JM

Hi again~ After i finished my class with you, my friend called me that she wanted to change our plan which was in day time tomorrow, so i can't talk to you tomorrow. On a second thought, it's better to attend the class in the morning so as not to absent. I will have my class in the morning from tomorrow. i heard if i changed time, the teacher would be changed. I just want to say thanks to you. thanks and regards [이름]

Great job on using 'on a second thought'!:) Oh, I you're very welcome... but wait, did you call the Korean manager about your class tomorrow? I hope you already arranged your schedule for tomorrow since I cannot fix your schedule. Anyway, have fun with your friend.:) -JMl

Here are your grammatical corrections:

After i finished my class with you, my friend called me that she wanted to change our plan which was in day time tomorrow,

>>>After i finished my class with you, my friend called me and said that she wanted to change our plan into day time tomorrow.

so i can't talk to you tomorrow.

>>>Correct

On a second thought, it's better to attend the class in the morning so as not to absent.

>>> On a second thought, it's better to attend the class in the morning so as not to be absent.
I will have my class in the morning from tomorrow.

>>>I will have my class in the morning from tomorrow.

i heard if i changed time, the teacher would be changed.

>>>i heard if i changed time, the teacher would be changed.

I just want to say thanks to you.
>>>Correct
thanks and regards
>>>correct