Where is release button by the gear shift subaru outback automatic transmission?

If you are referring to the shift lock release it is inside the console. Different years of Outbacks have slightly different locations for the access plug.

On a 2005 I just looked up there is a plug right above the "P" indicator. You pry the plug out with a screwdriver, insert the screwdriver in the hole and press down. Move the selector lever from "P" to "N", depress brake pedal and start the engine. Instructions including illustrations are in the owner's manual for your year.