Hi P-C-H,
To convert from a rollover Traditional IRA to a Roth IRA, it is a taxable event - how much taxable income you would like to pay income tax in the year of conversion.
IRS has a tax withholding estimator to help figure out if you have the right amount of income tax withholding from wages, pensions, IRA distributions etc. The tool asks about various sources of income, provides tips on tax credits and deductions, and estimates how much withholding to request or estimated tax payment to make. In your case, it would be additional income tax from the conversion.
Tax Withholding Estimator
https://www.irs.gov/individuals/tax-withholding-estimator
Or TurboTax Tax Calculator 2021
https://turbotax.intuit.com/tax-tools/calculators/taxcaster/
Or you can create a TurboTax test user ID using 2021 tax software to project 2022 tax liability - with IRA conversion or without.
Hope the above helps.