Step 1: don't panic. The same garbage rule that is going to cost anyone on a ACA plan thousands of dollars next year will also hopefully keep MTG's transphobic bullshit from becoming law.
Step 2: prepare to endure. Talk to your trans-kid's pediatrician or specialist NOW about roll-your-own HRT and puberty blockers. (You don't want the only person advising you on them to be an unlicensed internet pharmacist). Get a lawyer if you can or get in contact with your local trans advocacy group.
Step 3: prepare to move. Leaving a garbage red state for a brave blue state is good advice for anyone who isn't a white nazi. New York and New England or the west coast. Not VA, PA or MI (Both lovely, too purple).
Step 4: prepare to flee. Do NOT keep your family here if elections are cancelled, civil war breaks out, or the post-truno POTUS is an even worse Christian DominionIst.
Step 5: talk to your kid about what THEY want. Children are just temporarily disabled adults, and they may surprise you.
Step 6: vote. Pick Republican or Democrat, and vote in EVERY election, general or primary, whether you like the candidates or need to just spoil your ballot.
Step 7: advocate. As much as you can, tell your neighbors and reps and random strangers that your kid shouldn't live in fear or be tortured because some small-hearted bigot doesn't know the difference between sex and gender.