I'd recommend doing a 75% water change on the ten gallon as soon as possible, make sure the new water is the same temperature as the tank, and that you've added the right amount of water conditioner.
Then, is the outdoor tub that they were in still set up? Is there gravel or anything on the bottom of that tub? I'd move some of that into the tank, putting it into a mesh bag if you prefer not to mix it with the tanks substrate. I'd even take a big dollop of sludge from the tub, and add it to both filters. That should help seed both tanks with the nitrifying bacteria needed to process the fish waste, and get the tanks cycled faster.
Again, I am very sorry for your losses, hopefully we can help save the rest of the fish though, and you'll have more guppy fry coming along very soon I'm sure!