Just for information, you don't.
The DMCA mandates various actions on residents of the USA (both individuals and corporations). If you live in the USA, or if your company is registered there, you are bound by the requirements of the Act. But there is no requirement to be resident in the USA in order to serve a notice under the act.
I would add that filing a DMCA notice shouldn't be your first line of attack. It's something to do if a polite approach fails.
The following article might help: Dealing with copyright infringements of your web page or blog