If the above methods don't work, you can try using a chemical drain cleaner as a last resort. However, be cautious when using these products, as they can damage pipes or cause injury.
If the freeze is in an exterior P-trap (common in older homes), you may need to approach it from the outside vent or cleanout. how to unclog a frozen drain pipe
If you're not comfortable attempting to unclog a frozen drain pipe or if the problem persists after trying the above methods, it's time to call a professional plumber. They can: If the above methods don't work, you can