how do I certified a translated document?

It is great that INS told you that you may translate these documents yourself. In order for you to certify your translation you would have to create certifying statement. It can look something like that:

Names of the county a state

I, (translator's name) XXX

state and declare that I am competent to translate from XXX to XXX (languages), and that the attached translation of XXX(description of document) is true and accurate.

Signature of translator: XXX

State how many pages there are in a package.

(Notary information)

Collect a copy of your document, translation and notary statement and staple it together in order to make a package. Sign it in front of the notary. Since the notary will have to notarize your signature. And it would be important to remember that notary does not have to notarize the contents of the documents.

That's all. There are a lot of cases where government agencies would not accept personal translations. In that case you would have to get your documents translated by somebody else, either other person or agency.

A suggestion -

You ask your country's consulate in US to certify that your translation is correct.

Will you contact the closest representative of your country in US for the enquiry?

get it notarized