Unless you are very careful/lucky, the wear sensors are single-use only. There is a U-shaped spring clip that fits around the sensor head and holds it in the pad cutout. If that spring clip pinged off into the undergrowth when taking the old pads out, like mine did, then a new wear sensor is the only option.
If your sensor is loose then I suggest that means the spring clip is missing - that was how mine felt before I replaced it. This has nothing to do with contacting the wear sensor - mine was thousands of miles from making contact (I was upgrading the discs to S ones).