While trying to amend my return, I see that the IRS has already subtracted for the American Rescue Act but I don’t see the refund amount. Anyone dealt with this??

Do not amend for American Rescue Act.  

TurboTax Online does not give you a way to enter line 18 "as previously adjusted by the IRS".

This is a serious deficiency.

( You could call TurboTax  Support to find out if this is a true statement or there is a trick to make it happen.

I don't think so.)

After going through the amendment to get your new or changed forms and schedules,

refer to the IRS Forms page at www.irs.gov.

The blank form 1040-X in fillable PDF format and its instructions are available there.

Refer to the Instructions for what is to be attached to Form 1040-X.

Do not include your old 1040 nor your revised 1040 because the Form 1040-X reflects any changes there and becomes your new tax return.