If a lid fails to seal you must reprocess with in 24 hours. Remove the lid and check the jar surface for any nicks or cracks that you may have missed and also check the jar sealing compound on the lid you used as this may have had a small nick or cut in it and have been the cause of the seal failure. Always use a new lid and prepare it as you did in the first instance. You must also use the same processing time.
This means that the food quality will be poor as it will have been over processed but as this is the recommended method for health safety reasons that is what one should do. Personally if a seal fails then I refridgerate that jar or jars and either use with in a few days or freeze what I can’t use.