Yes, this can be changed if you do not qualify as a dependent.
If you could be claimed as a dependent based on the qualifying tests in the article below, even if your son did not claim you, you would not be eligible for the stimulus payment.
Check this link to confirm that you are not a dependent: Can I claim my relative or friend as my dependent on my 2019 return?
Both you and your son should amend your 2019 federal tax returns. If your state of residence has income tax, then the state tax returns, must be amended, too.
See this article for steps to amend a tax return: How do I amend(change or correct) a filed return?
Visit the following links for the most recent updates:
IRS: Economic Impact Payment Information Center
IRS Coronavirus Tax Relief
TurboTax Corona Virus Tax Center Updates
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