In the code below, how do I add a default value, so that if the settings are deleted from eeprom, a default value will be given?
How would they be deleted? If you don't provide code to delete what is in EEPROM, what is there is what you wrote last time.
If you want to ensure that data has been stored there before using what you read, you should add a char array to the structure, at the beginning. Test if what is read from the EEPROM is some specific value (your application's name, for instance). If so, use what is there. Otherwise, assign specific values to the variables.