Knowing Basis for Coverdell ESA Account

Hello,

 My oldest started college last year and I'm entering the 1099-Q on Turbotax.

  Turbotax is asking me for the basis for our Coverdell ESA for 2023, before we took our first distributions in 2024. I checked past statements, but our investment company doesn't appear to have record of the basis. We have contributed different amount different years. The account also changed custodians a few years ago.

  All of our distributions have gone towards qualified educational expenses.

  Does the basis have to be entered? Can it be estimated? Thanks! David