Back door roth conversion

Having trouble figuring out how to enter a back door roth conversion with desktop version of turbo tax. I made no contribution in 2025 and only did a conversion. 1099r received does not know taxable portion but i have 8606 from last year to use. Turbo tax did not prompt me for traditional value as of 31 december so it does not know my traditional value. Is this something I need to enter manually and over write the current draft 8606 for 2025 to get pro rated non taxable portion considered. If yes tell me where and how to do this

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