Your content on Postfity won’t be automatically migrated to Simplified.
However if you want to import your Postfity content to your Simplified account, you can export your content on Postfity, then with the generated CSV, bulk upload your content to Simplified.
Here's how you can import your posts in Simplified: https://help.simplified.com/en/articles/6535613-how-to-bulk-upload-and-schedule-posts-into-the-social-media-calendar