Updating an Object in LocalStorage Using JavaScript?

Edit - Updated JS code to display suggestions made in comments, still having issues.. Now the button <input id="edit" type="submit" value="Submit"> won't go to edit.html, instead it is returning action.html? It is nested inside of the editForm?

I have a simple form which I have managed to learn to submit, add, remove, and display bookings using the localStorage (thanks to those who helped on here!).

My last task is to amend a booking, I think I am almost there with it, but not sure how to call the indexes (excuse my jargon), to replace the values.

The form submits and the web address reads something like edit.html?OldFirstName=NewFirstName&OldLastName=NewLastName, however the values don't update in storage, and it throws an error saying

Uncaught TypeError: Cannot read property 'fname' of undefined`. 

I expected this to happen as I know I am not finding the values correctly, but I can't figure out how I should be writing it out? My thought process was that it would be similar to the original submit function but with the [i] values for fname and lname?

Here's my JS code - if you need anything else from me let me know:

// ~~~ add bookings to localStorage

var bookings = localStorage.getItem("bookings");

$("#submit").click(function () {
    bookings = (bookings) ? JSON.parse(bookings) : [];

    var newBookings = { 
        fname: $('#fname').val(), 
        lname: $('#lname').val() 
    }

    bookings.push(newBookings);

    var json = JSON.stringify(bookings);
    window.localStorage.setItem("bookings", json);

});

// ~~~ edit bookings in localStorage

$("#edit").click(function (e) {
    e.preventDefault();
    bookings = (bookings) ? JSON.parse(bookings) : [];

    var parent_form = $('#editForm');

    var fname = parent_form.find('.input:eq(0)').val();
    var lname = parent_form.find('.input:eq(1)').val();

    var newBookings = { 
        fname: fname, 
        lname: lname 
    }

    bookings.push(newBookings);

    var json = JSON.stringify(bookings);
    window.localStorage.setItem("bookings", json);

});


// ~~~ display bookings in browser

function showBooking(i) {
    var bookingResult = document.getElementById("result");
    var ul = document.createElement("ul");
    var bookingItems = JSON.parse(localStorage.getItem("bookings")) || [];
    bookingResult.innerHTML = "";
    for (let i = 0; i < bookingItems.length; i++) {
        bookingResult.innerHTML += `<div class="card card-body bg-light  m-4"> 
<h3>${bookingItems[i].fname + " " + bookingItems[i].lname} 
<button onclick="deleteBooking(${i})" class="btn btn-danger text-light ">Delete</button>
<button onclick="editBooking(${i})" class="btn btn-danger text-light ">Edit</button>
</h3>                            
</div>`;
    }
}

// ~~~ edit bookings in browser

function editBooking(i) {
    var bookingResult = document.getElementById("editAppt");
    var bookingItems = JSON.parse(localStorage.getItem("bookings")) || [];
    bookingResult.innerHTML = 
        `<form id="editForm" name="editForm" onsubmit="return editForm(this)" class="col-sm-6">
<div class="row">
<input type="text" class="input" id="fname_${i}" placeholder="${bookingItems[i].fname}" name="${bookingItems[i].fname}" required>
<input type="text" id="lname_${i}" class="input" placeholder="${bookingItems[i].lname}" name="${bookingItems[i].lname}" required>
<input id="edit" type="submit" value="Submit">
</div>

</form>`;
}

// ~~~ delete bookings from localStorage

function deleteBooking(i){
    var bookingItems = JSON.parse(localStorage.getItem("bookings"));
    bookingItems.splice(i, 1);
    localStorage.setItem("bookings", JSON.stringify(bookingItems));
    showBooking();
}

// ~~~ form submit handlers

function setAction(form) {
    form.action = "action.html";
}

function editForm(form) {
    form.action = "edit.html";
}