As a non UK resident, you do not need to report your overseas income on a Self Assessment tax return. Only your income and capital gains arising in the UK, should be declared on the tax return.
The residence page is SA109 and is used to declare that you are not UK resident, when you have taxable UK income. To submit an online tax return, that includes the residence, section, you need to purchase a commerical software, but you can only do this if you have a government gateway user ID and password.
If you are unable to verify your identity, you cannot submit an online tax return and will need to complete a paper tax return, which can be found here:
Self Assessment tax return forms