The first thing you want to do is make sure that the area around the door is clear so it can close. Empty the freezer and shut the door. If you no longer feel cold air escaping from the around the door seal, the freezer may be too full, or the items may need to be reorganized so that they do not put pressure on the door. Always store heavier items in the freezer compartment instead of on the door shelves.
Open and close the door carefully. If you feel or hear any catches or scraping, the cabinet may not have the clearance for your freezer model. If this is the case, you may want to exchange your freezer for a smaller unit or expand the cabinet.
Inspect the hinges to ensure they are not loose or damaged. If the door wobbles when you open it the hinges may need to be adjusted or replaced.
Next, ensure the rubber door seal did not get damaged when the freezer was installed. The rubber door seal is a rubbery gasket attached to the freezer door that helps keep the cold inside the compartment.
Check for rips, tears, or signs of wear. Replace the gasket if it is damaged.
If the gasket is not the problem, it is possible the freezer is not level. If your model has leveling feet, adjust the front feet so that the front of the freezer is at least half an inch (or 15mm) higher than the back of the freezer.
You can use a thin strip of wood under the front of the unit so gravity will help keep the door closed if your model of freezer does not leveling feet,
If all else fails, a child safety lock can help keep the freezer door closed until you get a chance to replace the unit or schedule a repair.