Trying to conditionally change text of off-canvas-toggle-label

I'd like to know which php function to use to change the text in the off-canvas-toggle-label conditionally (I am using a php $_GET(myparam) to know when I want to toggle the menu to an alternate text).

Basically, the off-canvas-toggle-label will say "Sign In" when you're not signed in and I want it to say "Sign Out" when you are already signed in (I'm not using wordpress for sign in...I'm using Sign In with Google, so I can't use a trigger based on wordpress sign in state).

So basically, what php filter can I use to grab the text in the off-canvas-toggle-label and change it?

Thank you :)