That CTC increase is not for 2020; it is for 2021. Your 2020 return does not have to be amended for it. More information will be available soon; the details of how it will be implemented have not yet been clarified fully. There may be monthly payments going out beginning in July 2021, with some of the CTC still left as a refundable credit on your 2021 tax return next year.
Basically, for 2021 only, the $2000 child tax credit has been increased to $3000 (or $3600 for children under age 6) and is to be paid by monthly check starting in July rather than as a credit on your tax return. So you would get a monthly check but your tax refund would be reduced.
Also, this is not permanent, it is only for 2021 due to the coronavirus “emergency“ unless Congress passes a new law to make it permanent.
Also also, there is no guarantee the IRS will be able to make the payments on time, and the law has an exception that allows the IRS to make the payments “as often as practical“ if it can’t meet the monthly requirement. No one really knows how this will work until July rolls around.