Looking for help on how to best migrate a wordpress page!

Hi everyone!

Im a beginner freelancer that just got a job to update the current existing wordpress page for a local materials store, I was having troubles updating some parts of the page because the plugins and the theme the page were design on where last updated on 12, as I was working on it I spoke with the client and told them that it would be better to renew the whole page to a new design.

And so they just gave me the approval but my problem is, can someone recommend me a course or a guide on how to export a wordpress page (the style I use is Divi) from my personal page to theirs?, and also how can I make like a backup of their original page so that if anything happens I can just restore it?.

Thanks everyone for their help!