First, make sure that your connection with Intervals is active in Settings - Integrations. It should show your connected account and Intervals user id.
Once it is connected any change in Intervals should show up in LeCoach. However this can take up to one minute. Refresh your browser if you want to force a the new Intervals data to show up.
If you are a Strava user, it could be that some of your activities are not showing up in Lecoach permanently. Click here for the solution.