Hello 'soyeuxdoux',
As 'hereiam' says, it is really important to ask about a combined shipping rate before buying. Some listings state very clearly what the combined rate is for multiples, some you have to ask, - and some don't mention it at all. So try to find out first if you can.
For now, though, you can send the seller a nice note asking for an invoice with the combined rate. You are unable to change shipping fees yourself. There is also a 'Request total from seller' link you can use, though I find the direct note to be more personable and friendly.
And whilst I don't like to say it, - if the seller refuses to offer a combined rate and you have bought items before asking, you could be expected to pay anyway.
If this is about the wrist bands, though, I am sure your seller will send a combined invoice the minute you ask. That is, if it is not done automatically at the checkout when you click Pay Now.