Hi,
A non resident landlord, needs to complete the residence section of a self assessment tax return, along with the income from property section.
To do this, you need to purchase some 3rd party commercial software. There is a list of commercial software suppliers here:
Self Assessment commercial software suppliers.
You choose your preferred supplier, complete their tax return which includes the residence sections and submit to HMRC.
The alterative is to submit a paper tax return, along with the residence and property supplementary pages by 31 October every year.
Thank you.