"net regular contributions made and distributions taken prior to 2020" for a 1099R for 25 yr old Roth IRA. Made sporadic depos. (<age 60) and wthdrwls (>age 60)?

1099R for withdrawal from Roth IRA prompts a request for net contributions and withdrawals made prior to 2020. We do not have 25 years of statements to answer this and for a $5k withdrawal getting bank and brokerage to find them would be impractical.
How should we enter.