Hi,
It seems that on your screenshot, you already have a coupon added, but you still have the interface to add a second coupon code.
HikaShop doesn't support having more than one coupon per order.
The only way I know to be able to do that is to use AWOCoupon Pro which modifies the coupon view of HikaShop to allow for it.
So if I'm correct, to change that text, you'll have to check with AWOCoupon support how to do it as I'm not sure.
Otherwise, I'll need more information on the situation on your shop to be able to understand what's going on.