First make sure Seven is connected to Fit by checking the toggle is on in Seven > Settings > Body Details > Connect to Google Fit. If it is and there is no syncing working between the two apps then, firstly after turning off Google Fit in Seven settings, wait for a few seconds, close the app, reopen and then try turning Google Fit back on in settings.
If that doesn’t work, check that Seven isn’t still connected in Google Fit ‘connected apps’, if you are, disconnect both Google Fit and Seven, close both, wait a few seconds and reconnect in Seven.
Lastly, uninstalling and reinstalling either Google Fit or Seven might also work.