Using Openwrt Snapshot r10077,I need help to configure a vpn like expressnvpn or ipvanish since I'm a newbie

Hi all,
I am grateful for this forum and I 'm here to learn, share, it is a fantastic group of sharing.
Since I am a newbie in this so I will need your support or guidance to help me install or configure a VPN like ipvanish or expressvpn in my router Linksys wrt1900acs v1, please.
The firmware I have installed is the:
OpenWRT Snapshot r10077-f54611b06d/ Luci Master (f138fc93)

Thanks for the precious time that will be used to help me here.