Access your router's web management page, 192.168.199.1 (by default for sabai router) and go to the "Network -> PPTP"
Now fill-up the L2TP Setup setting as follows and then click "Save"
Note: To see your server IP address, login here with your username and password.
Click "Start" to initate a VPN connection with RapidVPN
Check you WAN IP address. If you WAN IP address change then Your Sabai router is connected to the RapidVPN server.
To disconnect from the VPN server, click "Stop" and then "Reboot" your router again to disconnect completely