I can show you where Gentiles are NOT under the LAW that was given to a SPECIFIC people. Will that help any?
So Gentile should force Seventh day Adventist or any other Seventh day Sabbath keeper to observe Sunday then? Sunday worship is a man made ordinance and is not in the Bible. Err the Sabbath (Gen 2:3 And God blessed the seventh day, and sanctified it:) was given to man in Genesis before Abraham.