An easy way to test a magnet is to carefully use a compass.
Hold it at a distance from a very strong magnet and inch up closer until the needle moves to show either North or South. Don't ruin your good compass by getting it too close.
If the needle points to the north that is the side you use against your skin. Manufacturers label differently. So if you use one of their electronic magnetic pole identifiers, it will be the opposite. It will state South.
Better yet start with a magnet that is specifically used for health and not for industrial or home use that has been identified already. Some have covers or labels that are marked to tell you which side to use. Once you get a well marked magnet then you can use that magnet to identify other magnets that are not labeled by how they are attracted to each other.