Default Help Flashing Split View by Bigfau

I am wanting to install the LG G Flex Split View mod by Bigfau on my rooted LG G2 but I do not know how to "Flash in recovery and reboot."

Can anyone help me through this process? I was reading up on the flash guide here on the forum and saw that I needed a custom recovery installed before flashing. Is this really needed to just add the split view feature? If so, how can I go about doing this?

thx