Greetings Yoo Jina,

I have made the corrections in red below. Please be advised that speaking English is somethimes different from writing in English. So I made those corrections as well.

I apprecaite you reaching out to ask for assistance! This is a great way to take ownership of strengthening your English skills!! Way to go! We are hear to learn and grow! Keep up the great work! 

Teacher Luciana

I'm in charge of Administration with Online Sales Team at JDC Dutyfree Department.

I want to ask to (two) questions, if you don't mind.

I had a mistake. So I'm nervous.

I was in charge of Export at my previous company.

Teacher Luciana, Please check my sentences, if you don't mind.
I feel like so hard to make sentense for class. It is challenging to make sentences in class.
So write down here. So I wrote them here.