Samsung c430w colour laser print stuck on 6x4 paper size

[2550user]

Product.    Samsung  C430w  colour laser printer. (UK based).

[Personal Information Removed]

PROBLEM

Input paper tray,  papersize is stuck in 6x4 postcard size.

When trying to print from both Windows (wirelessly) or via AirPrint the papersize setting  (Tray 1 input tray) is stuck at 6x4 postcard size instead of A4.

There seems no way to set it back to A4 paper size.

The 6x4 stuck setting exists when trying to print (wirelessly) from any Windows Pc …or via AIRPRINT using an Ipad (ios14), or an iPad (ios15j or iPhones withios14 and ios15.   It is not therefore unique to AIRPRINT.   

When trying to print, the Printer Options boxes on the app or program being used at the time, show only a 6x4 paper size option and no others to chose from.  But all other options such as Colour/BlackWhite, or SingleSided etc are all fine.

WHAT I HAVE TRIED

1)   I have tried logging into the printer settings,  via browsing its IP addess on my network and look at Settings on the "Sync Thru" interface.   These Settings are very basic but shows "Tray 1 paper size" as 6x4.  ( CurrentSettings….System….InputTray) ….. but… there is no means to change this setting!!

2) I downloaded and installed Samsung Easy Printer Manager onto a Windows PC.  Ran this to try to change printer Settings, but this program simply sends you to the same process above, (Sync Thru browser interface) so no further forward.

3) check for Firmware update 

Printer has latest, uptodate firmware v3.00. (2018)

4).  I have made a careful visual mechanical inspection of the paper tray to see if something mechanical has been shifted or broken and is sensed by the printer and forces it to chose 6x4 paper.   Tray is in perfect physical condition and adjusted correctly for A4 paper.

It is as if the Printer internal setting has somehow stuck on 6x4 postcard as its paper size setting.

I have never selected 6x4 since have only ever used this printer with A4 paper.

This was a great printer but is now totally useless.  I have exhausted all my ideas.   
Anyone know how to get this back to regular A4 paper size???    
thanks in advance