Go to your Agora (It looks like a building surrounded by water)
1. If your in the city you had sent the CS from
A. Click on the Outside tab
B. You can click send them all back or certain amounts (for example to send them back at different speeds, biremes run different speed then light ships, transports etc)
2. If your in the city that is newly founded (highly discouraged at early game btw)
A. Send them all back
P.S. Your CS was destroyed in founding a new city.