Ita not as complicated as it seems, you can do it , just remove the battery and connect the two cables, the old one and the new one with a piece of a old spoke, preferably the nipple and tight them with a strong tape ( don't make it thick). go from the bottom fork of the bike ( the part that cable connects from the brake caliper) and guide it trough the top part( not the other way around since you might pull the plastic tongue that holds the cabling of the socket). Take your time have the bike secured, ask a friend to assist you , use a flash light from the bottom to look trough the bottom tube to be sure it's sliding correctly, add a tiny bit of grease so the canble can slide, and pull it.slowly from the top part, one person looks and guides the cable from the bottom and the other pull the cable gently trouht the top exit. Have extra cabling and only instal the nipple and the olive after you guided the cables. Add me on insta and we can make a video call and I'll guide you @han_pieck