People often say they have a double toenail, what has actually happened is that one or all of the three nail plates making up the nail have been damaged. The damage is permanent and cannot be reversed.
Thick toe nails are usually caused by repeated trauma to the toenail either from shoes that are too tight or a sports injury e.g. kicking a football.
Thick toenails are virtually impossible to cut with scissors. However, by filing the nail regularly 2-3 times every week when the nail is dry i.e. before bathing the nail will eventually flatten although it will never look like a ‘normal’ nail.