Hi HY Shing,
As part of the paper SA100 tax return, you would submit SA109 along with any other supplemenatary pages that are appropriate, at the same time.
Self Assessment tax return forms
The HMRC online version of the tax return, does not include the residence section.
For this reason, you can only send a tax return online, when you buy a commercial tax return and you have a government gateway user ID and password.
Please note that the whole tax return must be submitted in the same format ie paper or online.
A list of commercial tax return suppliers can be found here:
Self Assessment commercial software suppliers
Thank you.