You would need to determine your Roth IRA basis from your onw records of contributions. Those records include account statements, Forms 5498, Forms 1099-R for Roth conversions and rollovers from employer plans. If you ever took a distribution from your Roth IRAs, you'll also nee the Forms 1099-R that report those.
With respect to 2023, your Roth IRA can't be more than 25 years old because Roth IRAs did not exist before 1998 when they were introduced, so that's as far back as you would need to go to find records.
If you are over age 59½ and your first contribution to a Roth IRA was made before 2019, it's not necessary to know your basis because distributions from your Roth IRAs are qualified distributions.
