How to update an object in Realm Swift

Updating objects is just assign a value to a property within a write transaction. See our documentation.

https://realm.io/docs/swift/latest/#updating-objects

So you don’t need to delete and then add an object. Just assign new value to the property in write transaction like the following.

let workouts = realm.objects(WorkoutsCount.self).filter("date = %@", removeTodaysItem)

let realm = try! Realm()
if let workout = workouts.first {
    try! realm.write {
        workout.date = today
        workout.count = plusOne
    }
}

FYI: Please don’t use string interpolation in a query. Generally constructing an important string by string interpolation is bad practice. Use NSPredicate’s string substitute syntax like filter("date = %@", removeTodaysItem).