Set value on model when checkbox changes

I have a page which contains usnernames and checkboxes for every user. it looks like a matrix.

Now when changing one of the checkboxes, I want to change a value on the user, so I know which user is changed. This way I can check which users I need to update in the database.

My page-code looks as follows:

@for(var i = 0; i < Model.EmployeeList.Count; i++)
{
    <input type="hidden" asp-for="EmployeeList[i].Id"/>
    <tr>
    <th scope="row">@Model.EmployeeList[i].Name @Model.EmployeeList[i].Surname</th>
<th scope="row">@Model.EmployeeList[i].Location</th>
@for (var j = 0; j < Model.EmployeeList[i].SelectedSkillList.Count; j++)
{
<td>

    @*<div class="custom-control custom-checkbox">
        <input type="checkbox" class="custom-control-input" id="customCheck1">
        <label class="custom-control-label" for="customCheck1">Check</label>
    </div>*@
        <label class="label">
            <input asp-for="EmployeeList[i].SelectedSkillList[j].IsSelected" type="checkbox" class="label__checkbox"/>
            <span class="label__text">
                <span class="label__check">
                    <i class="fa fa-check icon"></i>
                </span>
            </span>
        </label>

    @*<input asp-for="EmployeeList[i].SelectedSkillList[j].IsSelected" type="checkbox" />*@
    @*If this is not included, prefix becomes null*@
    @Html.HiddenFor(x => Model.EmployeeList[i].SelectedSkillList[j].Prefix)
    @Html.HiddenFor(x => Model.EmployeeList[i].IsChanged)
</td>
}
</tr>
}