If you need to file an extension for US taxes and you have a foreign address, you need to print and mail the Form 4868 (link attached). Please check the box that you are out of the country and a US citizen or resident.
If you also have a state filing requirement, please go to the state tax website and see the state's extension requirements to see if a state extension must also be filed.
The address for mailing the federal extension is attached to the instructions.
https://www.irs.gov/pub/irs-pdf/f4868.pdf
