How to add multiple coc account in ipad mini?

I assume that you are asking about adding another Clash of Clans account to the iPad. Not everybody that reads your question is going to realI've what coc is supposed to mean. I'm just taking a guess.

You would need to use multiple Apple ID's in order to add another account. That's never a good idea. Purchases are tied to the ID used to make the purchase and you should stick with just one Apple ID.