Can a person blow a shofer with his left hand? If one sees one doing it on rosh hashana, should he mention it to the person? How much of an inyan is it?
The Shulchan Aruch (585) writes that this is preferable, but not essential. If it is easier for the baal toke’a to blow with his left hand, he should do so, for it is more important that the tekiah should be good.
See also Zayis Raanan 6.