Submission of a Change of Address online from an international address is not allowed. You will be required to fill out and submit the same change of address form you filled for a nationwide move at the Post Office in your area if you are relocating to a new address in another country.
In the event where you only remember to submit your Change of Address form after moving to an international home, then you can put a letter through to the Post Office in your old United States home as well as the new postal office in your new international address giving them an explanation on the situation.
Give them a clear direction on how and where you need your mail to be sent. The letter should also indicate any possible details requested on the Change of Address form (CPS FORM 3575).