STD UK Dom_1 and STD UK Dom_2

Hi
Please could someone help me.

My click and drop orders are not processing properly and automatically going into orders ready to despatch. I have spoken to them and they said some are coming through with STD UK dom_1 and some with STD UK dom_2. I havent a clue how to change this in shipping.

I do seem to recall an email about shipping times but like most Amazon directives it was as clear as mud to me. Could anyone advise please.