If I am working anymore and receiving survivor's benefits each month, living permanently, outside US do I need to file my income tax return earned from SSI only?

SSI is Supplemental Security Income.  SSI is not reported on a tax return.

Social Security Retirement/Disability/Survivors benefits are reported on a form SSA-1099 and the benefits received are to be entered on a federal tax return. The benefits may be taxable depending on the amount of other income you have entered on your tax return.
However, if the Social Security benefits are the Only income to be reported on the tax return, then there is no reason or need to file a tax return.

if Social Security Survivors Benefits is your only source of income then you do not need to file a tax return.