1. use commands for create and start the virtual TUN interface:
configure
set interfaces openvpn vtun0 config-file /config/mullvad.ovpn
commit
save
2. Firewall/NAT > Add Source NAT Roule
Description: ‘masquerade-vtun0’
Outbound Interface: ‘vtun0’
Translation: ‘Use Masquerade’
Protocol: ‘All protocols’
and drag the line to the top.