Changing text on Hero Slider / Overflow / Sub Heading /

I am completely new to the world of WebFlow having used wordpress for many years. I wanted to give it a go but already am hitting a brick wall.

I took a theme and decided to try learning how to change images / texts etc. I seem to not be able to change a sub heading text that is part of an overflow.

Can anyone point me to a tutorial that explains overflows / hero sliders etc. If anyone can give me the simple explanation as to why I cannot change the text that would also be greatly appreciated.

Thank you kindly,