Your delegates have access to a special property "index".
I refer to the link below for more explanation.

https://qt-project.org/doc/qt-5-snapshot/qtquick-modelviewsdata-modelview.html#models

But if you do something like, you can see it:

@ onValueChanged: {
console.log("index = " + index)
}
@

Changing the value of the model can be done like so:

@onAccepted: {console.log("accepted"); myModel.set(index, {...})}@

Also ListView has a currentIndex and currentItem property if you need those.

Good luck!

@ListModel {
id: myModel
ListElement {
name: "Speed"
units: "mm*100/s"
group: "conveyor"
mValue: "10"
mid: 0
}
....@

and my delegate consist of a TextField with:
@ onValueChanged: {
// Save the input
if(inputText != ""){
myModel.set(mid, {"mValue": inputText});
console.log(mid + "==" + inputText)
}
}@

I use "mid" to identify the index and the inputText then to save. I have it working alright, but I couldn't find a way to grab the current delegate index as wel.