First post, first time drawing, photoshopping and making a map. So it's a toughie.

I'm currently attempting to make a map made on Photoshop for a D&D campaign I'm DM'ing, so far I think it's pretty decent for a first time but I don't know how to do what I need to do now. On the top left quarter (that bit where it goes down) , I need the terrain should start elevating towards the east, effectively leaving 2 different heights in the zone. How would I get around that?

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Anyway hope you can help a noob. : 3 Thanks!