Read the thermometer calibration instructions that came with your new thermometer to learn how to calibrate thermometer.
Freezing point method
Fill a 4 pint container with crushed ice and water but not so much water that the ice is visibly melting. Allow a few minutes for the mixture to stabilize adding more ice as necessary. Insert the thermometer into the mixture and allow it time to register the temperature, If the temperature registers at 32º the thermometer is calibrated. If the thermometer does not show 32º it needs to be calibrated according to the manufacturer’s instructions.
Boiling point method
This method is not so accurate as the freezing point method because factors like altitude and atmospheric pressure will affect the boiling point of water. Put about 4inches of water into a container and bring it to the boil. Taking care not to have the thermometer too near the sides or bottom of the container measure the temperature of the water. It should read 212º. If there is a wide variance the thermometer needs calibrating but with a more accurate method.
Many thermometers cannot be calibrated but many digital thermometers can.