Step by step. Weight, food, workouts and spending on one page, on your iPhone and iPad.
Email ikmohamad19@gmail.com. It's one person, Ismail, in the UK, so a reply can take a day or two.
Say which iPhone or iPad you have and what you did just before the problem. If a sync didn't work, the app's Settings › Error log has a file you can attach.
On your phone, in the app. There's no account and no server. Settings › Export data writes everything to one file; Settings › Import data reads it back on another phone.
Check Bluetooth is on and the watch is near. If Garmin Connect is open, it may have the watch; close it and tap Sync now in Health. The watch sends new files a few times a day, so last night's sleep can take until mid-morning.
It needs iOS 27 and Apple Intelligence. On other phones, Log food shows Scan a barcode and Scan a label instead.
Settings › Delete everything, or delete the app. Both remove all of it. Nothing is kept anywhere else.