You may need occasionally to disconnect some or all connected users from the firewall forcibly. There are few ways I can think about to do so, for example installing Security Policy clears the cached authentication of the remote users, and while it does not disconnect them it will force a user to reenter his/her credentials. So, if you say want to disconnect a user you could expire it in SmartDashboard or change its password and then push the Security Policy.
But actually there is an easier way to do it : just go to the SmartView Monitor -> Users ->
click on any of the options: Users by Gateway, Users by Name, All Users, CheckPoint Mobile Users
and after finding the user you want to disconnect, right click on it and Reset Tunnel
Here is the screenshot of this procedure: