In order to identify/locate the currently offline devices, log onto iMonitor using your login details and click on 'Monitoring Points' and check for the offline devices.
The devices are typically cable tied within the monitored location (Fridge, freezer, walk-ins, etc.).You required to cut the cable tie and and place/tie the new device at any appropriate place within the location.
Steps to physically replace offline devices at your site.
Locate the offline device within the monitored area (fridge, freezer, walk-in, etc.). Devices are generally/usually cable tied at a desired/suitable location as shown in figure 1.
Fig. 1. Find device cable tied within your cold storage.
Clip the offline device using a pair of clippers or cutter as shown in figure 2. If not cable tied, just pull it out.
Fig. 2. Remove device using a pair of cutters/clippers/scissors.
Cable tie the new device within the same monitoring area/location.
Fig 3. Cable tie the new device by threading the plastic pointy end through the locking loop.
Replace the device within the software at the same time by following the instructions here