Hi Babigirl914, Welcome to the Community. We understand the disappointment of not being able to use your favorite apps on a new watch.
We noticed in the "About this app" section, the developer states it will be compatible with future models of the Galaxy watches. It may be they have not updated it for the Watch 6 yet.
Since they did not list an email address to be contacted, we recommend submitting feedback through the error report option in the Members app. Use this link for the steps for submitting the report: https://www.samsung.com/ae/support/mobile-devices/raising-an-error-report-via-samsung-members-app/