Trans men don't have male genitals. With the current medical techniques it is not possible to grow or build male genitals from a female body.
The majority of trans men have female genitals.
Some have cosmetic surgical alterations to mimic the external appearance of male genitals, with varying success and unfortunately very high levels of complication. These interventions are both very damaging to the body and even when successful, limited in what they can actually achieve.
HTH.