Yes, report it the same way that you would report receiving a 1099-DIV.
Yes, once your original return has been completely processed, you will need to file an amended return to include this income to your original return filed. Be sure to state on the explanation page that the income was reported to you on Form 1042-S, but that you are a permanent US resident.
The Form 1042-S is used to report several different types of income and you have to look up the code to see what type is being reported. The back of the 1042-S and the Instructions for Form 1042-S are very helpful in deciphering what to do with it.
Based on the instructions for the 1042-S, it is for dividend income from a U.S. Corporation.
Just add the dividend income and withholding reported to your U.S. individual income tax return.
Then, be sure you provide your information to the broker so you don't get it again next year. Generally Form 10442-S is reported on Form 1040-NR for nonresidents.
