If I don't have any achievement then how do I answer the question in the interview "What is your biggest achievement to date?"

I have one point you can deliver them (HR) that s/he might or might not like. I don't know. I haven't tried it.

I have one point you can deliver them (HR) that s/he might or might not like. I don't know. I haven't tried it.

Look, you don't have any major achievements. Okay. That's fine. Accept this fact in front of the HR. Then, say that

"this absence of my achievement makes me more hungry to have some and making those achievements under your esteemed firm will not only benefit me, but also to you too, sir! It's a win-win for both of us!"

You can try it out. See if it works. But do get some achievements, if you have time. It's never too late.