i don't kown how to thank you的回答是什么呢是NOT AT ALL 还是THINKING NOTHING OF IT

Not at all.是不客气的意思

Not at all. 不客气
My pleasure. 我乐意
My honor. 我的荣幸
Think nothing of it. 也可以，是别放在心上

换做是我，我会说

it's my pleasure!

意思是，能帮助你，我很开心

是NOT AT ALL 吧（不要客气）