This isn't so much saying what you should say but giving guidance (including info about the guidelines about size of file submitted!).
I am sure many on FWR feel confident about doing this but for those needing a bit of hand holding this might be useful!
womansplaceuk.org/2020/11/03/how-to-submit-evidence-wesc-inquiry-gra-reform/
They have given links to other articles and if anyone can suggest others hope you will ad them hear.