How can I change my ago once I have already filed my taxes

Once a tax return has been filed it cannot be changed, canceled or retrieved

You will have to wait for the IRS to either Accept or Reject your filed federal tax return.
If the return is rejected you can make the necessary changes and e-file again.  If accepted then there is nothing you need to change concerning the 2019 AGI

Age? AGI?  Was your filing rejected?

My name is Daniel  L Williams my age is 35. no my return hasn't been rejected the IRS accepted it I on February 7th and it is still being processed. I have read on the IRS site that if my is still being processed then I would need to change my AGI to 0. My AGI it's currently 50.