Locate the underside of the Schwinn Airdyne computer. There is a battery door located there.
Depress the latch on the Schwinn Airdyne battery door and remove the door. Remove both batteries from inside and discard.
Turn the first AA battery so that the negative end is inserted against the cone shaped spring inside the battery slot. The battery's positive end is marked with a (+) sign. Depending on the brand battery, the negative end may be marked with a (-) sign or not at all.
Push the first AA battery in place until it is snug inside the battery slot. Install the second AA battery in the slot beside the first battery.
Fit the battery door back on to the Schwinn Airdyne and push the tab down until it clicks into place.