I went to drain the oil out of my new 2015 Subaru Impreza but mistakenly drained the transmission fluid . Can anyone tell me if if I'd be able to drive it to the dealership? (it's less tan 10 miles). Thanks for the help.

NO! Is it a manual or CVT?

If it is a manual you will ruin it and the CVT won't go but you still might ruin it.

It's a CVT

Ruining a CVT will cost you a bundle. Flat bed it to the dealer.

You should absolutely keep yourself from doing any more work to this vehicle.

The 2.5i's CVT takes 5.5 qts fluid to refill. I'm not sure if the smaller Imp's 2.0i CVT takes less. regardless, go buy a $10 pump at Harbor Freight, 6 qts CVT fluid, jack the car up as flat as you can, and pump in the fluid. Then drive it to a proper horizontal lift where you can fine-tune the fill level. You CAN do this safely (or at least most folks can).

Forgot to mention that the check/fill bolt is on the SIDE, and HIGHER up (obviously) the CVT. You'll be able to stick the pump's plastic hose in there to fill the trans. Wear gloves...LONG ones!

I put 10w20 in my2012 Subaru Impreza, didn’t realize it needed a 0W 20 what should I do

Where's you find 10w20? Perhaps you mean 5w20 or 10w13/40? Regardless, it'll be ok...especially in the summer. See other discussions re why the international spec 5w30 is better than the Nortth American 0w20 spec anyway.