What’s the best way to remove dried baby shampoo and water from the back of a 2021 Honda Accord?

Answer 1: Spray isopropyl alcohol in the hard-to-reach spots, then follow up with a scrubber. Next, spray down once again with alcohol and finish by letting the entire area air dry. It should be clean.  Answer 2: You can try stapling velcro to a paint stick or ruler and use it to scrub the shampoo if the area is hard to access.  Answer 3: Simply pull the deck and wipe it thoroughly. The entire job should only take a few minutes.