If you have already filed your return and it has been accepted, there is no way to change the refund to direct deposit from being mailed.
If you are wanting to make the change so that your stimulus payment is direct deposited. There will be a portal open by the IRS in a few days where you can enter direct deposit information for the stimulus payment. Use this link to track its availability: https://www.irs.gov/coronavirus/economic-impact-payments