The option to choose your position appears during account opening; however, you can also change it at any time.
Log in to Fidelity.com and select your Fidelity HSA account. In the Positions tab, select Core or FDRXX.
Select the Change core position button.
Select FDIC or Fidelity Government Cash Reserves (FDRXX), then click "Preview order," and "Submit."
Switching is free and will not change your ability to access or invest this money.