How to Apply modifiers on Order Header level and Create using API?

I'm totally new to this adjustments/modifiers. I need to apply adjustments at Header level not on line level and in case if modifier is not exist have to create, Please suggest proper approach.

Now,I have to apply adjustments on Order Header level only, can you please suggest of paramerters NEED to pass.

Can you please tell how to check if the discount is applied on header level after above step? ,.

Please I'm trying to pass parameters like this for adjustments .

FOR h IN order_h_info

LOOP

l_header_rec := OE_ORDER_PUB.G_MISS_HEADER_REC;

l_header_rec.TRANSACTIONAL_CURR_CODE := h.currency_code;