The lock is able to rekeyed but it is fundamental to have at least one working key.
The use of the above pictured reset tool is required to make a key when all existing keys have been lost.
First, the door it is fitted to needs to be unlocked. The lock must be dismantled and the cylinder removed.
The cylinder is then inserted correctly into the cradle and the actuator turned to the reset position. Insert a new precut key and rekey to same.
Remove cylinder and replace in lock.
In future, you can still rekey this lock provided you have at least one working key.
See also Kwikset Smartkey Fault