Look for a label or sticker somewhere on the equipment. If you find a label, call the phone number provided.
If the label has worn off or you can't find one, here are some suggestions.
If you've received equipment due to an injury, contact accessable. They issue ACC rehabilitation equipment.
You can find contact details on their website.
If you have Ministry of Health equipment, contact the equipment provider for your region.
See: Who provides Ministry of Health equipment services?