You uninstall Yarvi in Shopify admin under Apps, like any other app. Shopify ends your Yarvi subscription when you do.
Uninstalling also removes Yarvi's access to your store at once. Yarvi keeps no access token after that.
Shopify then asks Yarvi to delete your store's data, about 48 hours after the uninstall, and Yarvi deletes it when that request arrives. If you reinstall before then, your data is still there.
For any other question about your data, ask in Help in the Yarvi app and it goes straight to Ned.