❔ How to convert from one type to a different type

I am still a week or so old in C# so still learning :). Please be patient if I misunderstand.
I am using the Autodesk Revit API to create an Addin.

I have a windows form with a list and will update colour if element is selected.

            //ElementId is type
            //selectionList.SelectedItem is a list of string vals and then get current item. Without ToString() its an object.
            string curItem = selectionList.SelectedItem.ToString();
            ElementId curItemId = (ElementId)Enum.Parse(typeof(ElementId), curItem);
            //curItemId error: type provided must be Enum. Parameter Name: Enum Type.

            Autodesk.Revit.DB.Color overrideColor = new Autodesk.Revit.DB.Color(52, 235, 85);
            updateSequenceInOrderedSelect.OverrideColour(uiapp, curItemId, overrideColor, false);  

I need to convert from string to a new type called ElementId as my method after this requires this. How do I do this? I used this as ref: https://stackoverflow.com/questions/60405465/cannot-implicitly-convert-type-string-to-autodesk-revit-bd-displayunittype

The list is generated from ElementIds converted to string. I want to use whatever is currently selected, convert from string to ElementId, then override the colour to make it clear to the user which is is selected currently.