1. Enable login on FortiAP

To enable telnet from the FortiGate CLI, please run the following commands :

config wireless-controller wtp
edit FAP220Bxxxxxxxxxxx (Serial number of FortiAP)
set login-enable enable
end

2. Telnet to FortiAP

exec telnet x.x.x.x <- IP of AP.

3. Save Config / Factory Reset the FortiAP

cfg -c (save the configuration)
cfg -x  (Factory reset the FortiAP)

cfg -e (list all configuation on screen)

FortiAP CLI

http://help.fortinet.com/fos50hlp/54/Content/FortiOS/fortigate-wireless-54/reference-fortiap-cli.htm