A heat gun or hair dryer will usually work, but you may have to run an extension cord out to your vehicle. Another option is to use hot water, but be conscious of the current temperature. If it is still below freezing, you should not use water as it may refreeze., Look at your service manual to see which wheels the parking brake holds. Then use your heat source to apply heat to the brake cable and the calipers/drums at that wheel. You should apply the heat long enough for the brake components to be warm to the touch. The amount of time this takes will vary based on how cold it is outside.

This will have to be done from underneath the vehicle so you may need to lift your car.
For safety reasons, you should turn off your engine and chock your wheels before getting under the car.
 After applying heat to the brake system, immediately try to release the brake. Do not give the braking components time to refreeze.
Locate an appropriate heat source.
Apply heat to the brake components.
Try to release your brake.
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