That will depend on the cleanliness of the oven. If the oven was clean and the milchig pan did not come into direct contact with any fleishig residue, the pan remains Kosher. However, if the oven racks were caked with presumably fleishig grease, the pan must be considered treif.
Generally speaking, something that became treif in an oven would require Libun Chamur, heating to the point of glowing red-hot, which is generally not practical to do. Here where the pan is Teflon coated, this is completely impossible and the pan must be disposed of, if the oven was dirty.