Notifying UKVI of address change - What to put in the "Previous postcode" field

I am seeking to update UKVI my address for the first time through the online form provided at The form requires me to input my old UK postcode (the one currently on record with UKVI).

This is my initial attempt to update my address with UKVI. Prior to my current address, I resided in various Airbnb accommodations upon my arrival in the UK while searching for permanent housing. During this time, I did not inform UKVI of my Airbnb addresses.

I’ve recently updated my address with HMRC (the tax office), but I’m uncertain if this information is shared with UKVI, so I’m unaware of the address recorded by UKVI.

Has anyone encountered a similar situation? What did you enter in the “old UK postcode” field? Additionally, is it acceptable to select the checkbox indicating, “Please select this tickbox if you do not have a previous UK postcode,” or is there a method to verify the postcode currently held by UKVI?