This isn’t the first time MTN is browsing free without any VPN, it usually last for a couple of days before it eventually stops working.
So if you have a MTN SIM with you, all you need to do is to insert it into your phone and start browsing. No special settings is required.
Keep in mind that this can stop browsing at anytime. So incase it stops working, you can try the MTN unlimited free browsing with either Stark VPN Reloaded and Ha Tunnel Plus VPN App.