A thermometer pressed against the cold rear wall does not represent food stored in the centre. Choose a suitable fridge thermometer and follow its instructions for placement and settling before interpreting the result.
What the observation tells you
The purpose is to learn about the storage space, not to hunt for the coldest possible spot. Keep the thermometer away from direct contact with cooling surfaces, freshly added warm containers and a frequently opened door. A quick reading taken while holding the door open mostly adds uncertainty. Note the location so later measurements can be compared fairly.
A useful next step
Check the manufacturer's recommended arrangement and keep the door closed between readings. If food safety is already in doubt, arrange suitable alternative storage while investigating. Moving the thermometer repeatedly until it shows a reassuring number does not establish that the rest of the fridge is maintaining an appropriate temperature.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.