Hello Doris, You really don't want to get an adpater for this, (even if you could find one - they're not at all common) since the thickness of adding in an adapter would make the dryer stick out further from the wall, etc.
What you need to do is to get a new "pigtail" for the dryer that has the three (3) prong plug that matches your 220 Volt-AC wall outlet. These are available at most Home Depot, Lowes, Sears, or at any appliance or Hardware store. They don't cost all that much and will provide you with the correct plug and cord set for your house's electric dryer outlet.
The four (4) prong cord & plug has a separate ground wire in them, while the standard thre (3) prong plug uses the netural as the ground, or has a separate green wire running from the dryer cabinet to either a grounding screw on the wal plate, or to a ground ******** a water pipe (typically found in older homes)
Just be sure to unplug the dryer before changing the cordset out for the 3 prong one. Make sure the power is also off at the breaker panel too. Now at the rear of the dryer there is a small access panel where the cordset goes into the dryer. Remove that panle and you'll see three (3) connections on the panel along with a Green Grounding connection.
The connectors that get the power are the outside connectors, these are "HOT" and get 120 V-AC each (120 x 2 = 240 Volts AC) while the connector in the middle is the NEUTRAL connection point.
The wiring is straightforward and there should be a simple wiring diagram either on the access panel or the connection points should be labeled for each of the wiring fasteners (screws or nuts)
Just be sure to get the fasteners tight, and the new 3 prong cordset you buy should be long enough to reach from the dryer (when it's pulled away from the wall) to the house outlet. Typically they come in either a 3-4 foot length or the longer ones are 5-6 feet long. If in doubt, get the longer cordset. You can also check the wrapper of the new cordset, as they provide a simple wiring diagram also, to help you install it correctly.
Just be sure to add the included strain relief, as instructed, onto the cordset and put the access panel back on when you're done and you'll be all set to use that "new" used dryer!
I hope you find this Very Helpful and best regards!