The only transportation help that Medicare pays for is an ambulance. Medicare can pay for some non-emergency ambulance service from home to a medical treatment such as dialysis, but only when a doctor has prescribed it because any another form of transport wouldn't be medically advisable. If there's no medical need for an ambulance, Medicare won't pay. And if an ambulance isn't necessary, Medicare won't pay for any other transportation help.
But there may be local transportation assistance services that you can call on. Local senior transportation services often have specially equipped vans and personnel to help transport a frail elder to and from a medical appointment. An excellent resource to find such transportation help is the web site of Eldercare Locator operated by the U.S. Administration on Aging, or you can call them toll free at 800-677-1116. You can also look for transportation assistance at the National Council on Aging's web site called BenefitsCheckup.