Change Country on Child Iphone 6 IOS 12.5

Hi There,

My youngest uses an older generation Iphone 6 with IOS 12.5 we have just recently moved countries.

The rest of us have succesfully converted but my youngest phone seems almost impossible.

I have searched high and low and cannot find a workable solution to amend the country. The settings menu is different so you don't have media and purchases and his name is greyed out.

Any suggestions would be greatly appreciated.

Thanks