If my parents claimed me as a dependent on last year's taxes, how do I show that on this year's taxes?

You don't.  There is no way to enter on a current year tax return that you were claimed as a dependent on a prior year tax return.

If you are being claimed as a dependent on your parent's 2023 tax return and you are filing your own 2023 tax return then you Must indicate on your tax return that you are being claimed as a dependent.

You don't.  If they are claiming you this year, you mark the box that says ''someone else can and will claim me''.    But if they are not claiming you this year, you don't need to indicate that.