A bicycle pedal turns thousands of times while its bearings receive little attention from most riders. For Shimano SPD-type pedals, begin with a simple inspection: make sure the fasteners on the pedal body are secure, spin the pedal and feel whether it turns smoothly. Roughness or binding calls for a closer look. Then check whether the body rocks noticeably from side to side relative to the axle.
A little movement can be normal in this type of pedal, but excessive play points to bearing adjustment. It is also important to distinguish movement inside the bearing from a loose connection between the pedal and crank. On serviceable SPD designs, the bearing unit can be removed, cleaned, greased and adjusted, but the work needs tools suited to the model. Left and right units differ, and their thread directions can be counterintuitive, so working on one pedal at a time helps keep parts in order.
Not every bicycle pedal can be maintained in the same way. Some bearings are adjustable, while other models are not intended to be opened for service. Identify the exact model and its service options before dismantling anything. For the rider, the useful habit is to check from time to time whether the pedal still rotates smoothly and whether play has increased. Catching a change early may allow an adjustment or repair before pedalling feels poor or the entire pedal needs replacement.