Postal code Map - Combining groups of postal codes

Hi all,

I'm trying to create a map visual based on US DMA codes, here's info on what dma's are. It's litteraly a group of postal codes that are identified as one area. 

I'm trying to create a map visual that shows e.g. sales by DMA, so all postal codes per DMA will have one total sales value and need to be grouped. Like you see below.

Any instructions how to do this?

Thanks!