Migrating page.details from one theme to another on Shopify?

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Through my team editing some code (trying to upload custom fonts), my original website got quite messed up (it was going to cost a lot to fix), and the duplicate was not made/backed up until afterwards. I had decided to restart with my theme (Flex-Bloom from Out of the Sandbox). I uploaded a new one and finished making all of the design edits within customizing the theme for my home page/layout, including implementing the new custom fonts, and just needed to make sure the other pages worked from there.
With my original theme file, I had made some page.details templates and had filled in the sections in detail. I am now seeing that once I publish my new version of my theme, these templates are no longer available for the same pages for which I had them assigned. Is it possible to migrate the page.details templates with content over to my new theme or do I have to create them all manually again?

I'm not extremely experienced in coding/CSS FYI (a fashion designer by trade) so I'm doing my best to figure this out! Thanks.