Select "Pay with HSA/FSA Funds" to trigger the Letter of Medical Necessity flow and qualification survey. When entering payment details, use the HSA/FSA tab for your Thatch card, or the Credit/Debit tab if you're paying with a personal payment method and will file for reimbursement later.
Don't worry—choosing "HSA/FSA" doesn't require you to have an HSA; your CHOICE plan qualifies for this option.