Can you elaborate little more on what exactly you want to do?
Typically, we have 2 modes of deployments:
1) AP controlled by a Fortigate
2) AP managed by Fortinet Cloud
If you want to make AP as client mode and connect to your existing wireless network, we can support that by meshing 2 221E's together
221E(root)----------wireless mesh-------221E(Leaf)----Wired PC