Yellowing Vinyl Floor

Hello, A friend of mine put some type of substance a few years ago on his vinyl floor. The floor was white but needed a bit of shining up, so therefore the need to shine it up. Don't know what he put on - it wasn't wax, maybe some type of urethane stuff. Anyway, over the years, it turned very yellowish and now looks awful. Any suggestions for removing or stripping this stuff off? Hopefully it didn't penetrate into the vinyl and could be easily wiped off or stripped off with the right material. Wish I knew what he put on, but can't find it. Looks like it would be easy to remove and at least get back to the original white underneath so that it doesn't look like a dingy yellowed mess. Thanks for any input or suggestions!
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