CustomLoginDemo into a TabbarController

Hi Chris and team,
I’m a TOTAL novice to APP development but, I’ve completed the Firebase Authentication tutorial and have customised for my sports app. I can’t seem to get the login or sign up screens to jump into a tabbarcontroller of one of the tabbarController’s associated viewContollers without losing the tab bar navigation elements in the process. I have tried setting the tabor controller identity as HomeVC hoping the constants.swift file would send it there, but causes a black screen in the simulator. Help please?
Thx Rob.