Thank you all for your helpful comments. I finally figured out the recommended way of the owner's manual by looking behind the lighting unit where two collar nuts are located. Just unscrew them and the lighting unit cover can be removed, including the lens without any prying.
I also upgraded the license plate bulb to a LED bulb compatible with 194 or 2825.
Since I purchased a pair of bulbs and used only one, if anyone would like to buy the 2nd bulb from me for $5 (shipping included), PM me. (The pair cost $22)