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Hello @HelenCY. thanks for joining the Fitbit Community, it's great to have you on board. 
Usually when a tile is not showing in the Fitbit app is because of two different reasons:
- Your tracker has been removed accidentally from the account: To check this, please tap on the Account button and verify that your tracker is listed under your Name. If it's not, please set it up as a new device:
- Open the Fitbit app and tap on the Account symbol at the top right corner of the screen, then tap on "Set up a New Device"
- Choose your tracker and follow the onscreen instructions to continue
- The tile has been removed from the Dashboard and is not invisible: To verify this, please scroll down until you find the Edit button. Tap on it and the invisible tiles will display a plus sign on the top left corner, tap on the plus sign to make them visible again.
I hope this can be helpful, give it a try and keep me posted in case you need anything else. 
Best Answer