Script to show text if cell value is below zero, otherwise show the calculation

I am completely new to scripts and don't know where to begin, so I hope I can get a bit of help here for this one time task that I have.

My problem is as follows:

If cells in my calculations in column G show values below zero, I would like to write a text message "No help required". But if the value is above zero, the cell should show the value of the calculation.

Any help is appreciated.