I'm not exactly sure what you mean, and am trying to picture the kind of appliance you need. But, I suggest you go to a medical supply store and see
if they can help you find a support that works with your toilet. You may need to bring a picture of your toilet, or any paperwork that might help.
Another idea is to contact the manufacturer of the support you purchased by telephone or email to see if they're willing to make an exchange -- and to help you identify what you need. (I've had luck with this when dealing with the wrong or malfunctioning parts.) Search for the manufacturer's corporate office with an internet search using the exact name. Then look for "customer service" or "customer relations" links. You can usually call (most big companies have toll-free numbers) or email. You can also try to get a toll free number for the company using toll-free directory assistance, 1-800-555-1212. Many times companies are willing to repair or replace items if you contact them and describe your situation. It helps if you have the receipt. (Sometimes this is required.)
Finally, you can always try your local hardware store to see if they have ideas for attaching the support you have. Again, you may need to bring in a picture or diagram. Even large chain hardware stores seem to try to provide good customer service. Good luck.