What Is a Biblical Case for Submitting to God’s Good Design for Our Bodies?

Questions about how to make a biblical case for God’s good design in creating two genders and the rightness of submitting to his design for our own bodies, and how “gender-affirming” care can be wrong if it’s not discussed in the Bible.  

• Would you make a biblical case for God’s good design in creating two genders and the rightness of submitting to his design for our own bodies? My trans, Episcopal brother is asking why “gender-affirming care” is wrong and harmful if it’s not discussed in the Bible.