Which Kündigungsfrist is applied?

Which Kündigungsfrist is applied: the one valid at moment of handing in my notice or termination date on that notice?

Hello, I have the following question: The Kündigungsfrist of my contract changes after being employed for 2 years, from '6 weeks till end of the month' to '3 months till end of the quarter'. I want to quit after the 2-year moment, but hand in my notice before that moment. Does the moment of handing in my notice count for which Kündigungsfrist is valid or the requested end date in my notice.

For example, 7th of February I am employed for 2 years. If I hand in my notice on 6th of February, do I use the '6 weeks till end of the month' or the '3 months till end of the quarter' notice period?

Thank you so much!