If you have a need to disconnect a user from the firewall forcibly. There are a few ways I am aware of that will force users off the VPN.

Installing Security Policy (link)-  clears the cached authentication of the remote user, although this doesn’t seem to disconnect them it prompts them to re-enter credentials.

Expire the user with SmartDashboard or change the user’s password and then push the Security Policy.

Logging into the console of the firewall and using the vpn tu command to disconnect users.
(link) – VPN Commands:  (link)

My favorite method is to SmartVire Monitor:

Open 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.