I haven’t received my child tax credit even though I qualify for it how do I go about it

Are you asking about getting the child tax credit on your 2020 tax return or are you asking about getting the monthly advance payments?  Please clarify----and tell us how old your child(ren) will be at the end of 2021.  Did you file a 2020 tax return?   Has it been fully processed?

Am taking about the monthly advance payments

https://www.irs.gov/credits-deductions/2021-child-tax-credit-and-advance-child-tax-credit-payments-frequently-asked-questions

According to the IRS if your return, even an amended one is still processing then  you will not receive the advance child tax credit payments.  Go to topic Q B 12  as of June 30th there were 35 million US income tax returns that had not been processed and estimated only 3% of phone calls were being answered. Verify that here