Help requested - Unrooting HTC One M8

[WestIsBest]

Greetings all. I've just purchased a 'factory refurbished' device and have found it has been rooted. I wish to return it to its un-rooted state. All this is new to me so I've done a bit of research but have not tried to do much yet. I have used Hasoon2000's toolkit to run the 'Getvar All' command and I got these things back:

modelid: 0P6B13000
cidnum: 11111111
version-main: 4.28.502.1

If I look in the phone settings for software versions, I also see "4.16.401.10".

My plan was to install the TWRP recovery and then follow a guide such as this:
http - theunlockr.com/2014/06/08/how-to-unroot-the-htc-one-m8-video/

The problem I have is choosing which software to download for the restore. The cidnum of 11111111 and modelid are confusing me. I understand the cid indicates 'SuperCID' which may cause no probs but I also gather that the modelid indicates that this device was originally T-Mobile in the US. I am in the UK.

So basically, are there any issues I need to be aware of and is my plan of action correct?
Grateful for any assistance received.

 

[Rukbat]

The normal way of "unrooting" a ROM (that's what's rooted - the ROM, not the phone) is to just flash the stock ROM to it. Your problem seems to be determining just which ROM that is. Searching the ROM numbers further, you may find that it's a TMobile ROM, in which case, you stick with a USA TMobile ROM.