oreo1912,
Move the lever to the remove position then gently work the plate out. After you get get all the area clean, pry up the lock thing and pour the oil into it's hole. Then turn the machine on it's back and oil it from underneath as well.
I have two 500a's and both of them had sticky needle plate locking parts. It took a lot of oil, I used Tri-Flow, to get them unsticky.
Joe