After tax 401k in plan conversion to Roth 401K

My company plan permits after-tax conversion to the plan Roth 401K. The after tax contributions have been sitting in the plan for 5 years and have earnings. My questions are:

1- When I convert a portion of the after tax money to Roth 401K, will it force me to also convert a portion of the earnings?

2- If yes, who determines that earnings portion and how it is reported to me next year so I pay the corresponding ordinary income taxes in my tax return?

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