Can a Noahide pray using Tehillim (Psalms)? Rabbi Yaron Reuven gives guidance on the best way to pray for non-Jews that don't plan on converting to Judaism. Everyone can and should pray using Tehillim. Jews have to pray using the Siddur, and non-Jews pray from their own heart or using Tehillim, but should not pray using a structured prayer book.

Any organization that is selling Noahide Siddurs or anything like it is one to stay away from. In over 3300 years since Mount Sinai there has never been anything like what's been happening recently with many Noahide organizations. It's forbidden to create a new religion, and by publishing prayer books and establishing various other quasi-Jewish religious practices, that's exactly what it is.