If you want to migrate content from or to a Plone site it is always the best use of ressources, if you ask volunteers to copy and paste the content items from one environment to another ;-(
But seriously: The Plone community created a tool for such tasks with a funny name: ‚Transmogrifier‘. You could find some information on this at https://docs.plone.org/external/collective.transmogrifier/docs/source/index.html#transmogrifier and a training session at https://training.plone.org/5/transmogrifier/.
But it is not that easy and fast to create pipelines and blueprints for a migration yourself. Thus I recommend to ask and pay a Plone professional service to do the migration. It would preserve your nerves and you get results very fast.