Override old object in array swift ios

I have an array of custom objects. For simplicity, lets say each object has 3 properties : id, timestamp and text. I am now obtaining a JSON response from my server which contains updated text for my objects in the array. I need to do the following :

1. Obtain the object with the given id from my array.
2. Set the text of the object to the updated text WITHOUT changing any of its other properties.
3. Override the old object with the new and updated one.

I have found the following extension which allows me to find the object in my array.

 extension CollectionType {
func find(@noescape predicate: (Self.Generator.Element) throws -> Bool) rethrows -> Self.Generator.Element? {
    return try indexOf(predicate).map({self[$0]})
}
}

I am then using the following logic to obtain the item from the array.

let my_object =  questionImageObjects.find({$0.id== myId})

Now I set the text using my_object.text = currText.

The last step is to override the old object in the array with the updated one. This is where I am stuck.