I need to amend my 2023 tax return. I must have filled it out wrong because I supported my granddaughter and my return was “0” HELP

If your only income was Social Security, then sorry, but you are not eligible for child tax credit.  You must have income from working to get the Child Tax Credit.   For tax year 2021 only, you could get the CTC even if you did not work, but for 2022 and 2023, the rules went back to the "old" rules----if you do not have income from working you cannot get child tax credit or earned income credit even if you are supporting a child.   Sorry.

Did you file and was it Accepted?  Did you have any other income?  If you only entered Social Security you would not be able to efile.