Help please amending Asda online order to "no substitutes"

Si_Clist

Can't get through to customer service and a search here hasn't found the answer so ...

I've completed an order online then noticed on the confirmation email that I didn't disallow substitutes.  Not surprising really, because I didn't notice an option to do that!  Now I've completed the order, how do I amend it to "no substitutes", or better still, give me the choice of subs or not for each item?

Si_Clist

Just managed to get through to Asda customer service and learned that it can't be done.  Fair enough.