Notice period… what do I enter?

Hello, I would like to apply for a position and in a form I can specify the notice period for the current position with a calendar for manual selection.

In my employment contract, I have a notice period of four weeks in accordance with Section 622 of the German Civil Code (BGB).

The employment relationship of a worker or employee (employee) may be terminated with a notice period of four weeks to the fifteenth or at the end of a calendar month.

In the fill-in field, I can only select one date. What should I base my choice on? Should I choose the end of this month (May 31, 2024) or, for example, July 31, 2024, if I include the interview (I haven't received an invitation for that yet).

Can you help me here?

Thanks!