Cannot access Synology DSM after setting up VPN client with Use default gateway on remote network

I wanted to use my Synology NAS as a VPN gateway, so I've setup a VPN connection and wanted to share it with my LAN. I checked "Use default gateway on remote network" and "Reconnect when VPN connection is lost" and accidentally pressed "connect". I immediately lost connection to DSM. Now I'm unable to acces my NAS to turn off the VPN connection and use it normally again. I've already turned my NAS off and on again.

What can I do to acces DSM?