Filed 2018 return thru CPA and have received my refund. For comparison I ran my number thru Turbotax. CPA used Std. Ded. Turbo used "Itemized" and had a larger refund?

If I filed my 2018 returns thru a CPA can I now amend my return to use Itemized deductions instead of the "Std Deductions the CPA used?  When i ran my numbers thru turbotax for comparison it recommended using itemized deductions for a larger refund.  What can I do next?