Conversions are made in a taxable year, not for a taxable year. The Roth conversion is independent from the traditional IRA contribution (except for the fact that the basis in nondeductible traditional IRA contributions gained from making the contribution for 2019 affects the calculation of the taxable amount of any subsequent distribution from your traditional IRAs); the association of the contribution with the conversion exists only in your mind. The Roth conversion has nothing to do with your 2019 tax return.
