In newer software versions, you should be able to control the wipers with the left scrolling wheel, right after you have activated them with the push button on the left arm.
https://www.tesla.com/ownersmanual/modelx/en_us/GUID-A5C33F3....
https://www.tesla.com/ownersmanual/modelx/en_us/GUID-A5C33F3....