@cedwards8511
So, when you click on an item in ArcGIS Online Assistant, it has two boxes on the right. The first one is the Description of the map, application, etc. The second is the Data, which is the one you would be interested in if you are trying to do what I did.
In case you're not familiar with the JSON, all the layers in the map are located near the top in the "operational layers":
"operationalLayers": [{Layer1},{Layer2},{Layers3}, ...]
If you're just trying to replace one layer, you will need to find that layer in the operational layers and then replace it with your replacement layer. If you don't have too many layers, it should be easy enough to just scroll through. If you have a lot, you'll probably want to collapse layers so you don't have to scroll through them all (This can be done by clicking on the carrot arrow (^) to the left of the line of code).
Once you find the layer, you'll want to delete it. Easiest way is to collapse the layer and then you just have to highlight the "{<-->}" and delete that instead of trying to scroll all the way down and possibly end up deleting another layer.
Then, you copy the layer from your other map by basically doing the same above and then pasting it into the spot where you deleted the previous layer. You'll probably want to do this step first though and copy the layers text into a notepad or something to have it on hand so that you don't have to find where you deleted the previous layer again. That said though, probably not a big deal as you could just paste it anywhere and then re-arrange it in the map.