Uploading an XML form

1. What is the issue? Please be detailed.
I am a complete novice and am trying to implement a slight modification of a previous form that my assistants prepared for me. I have downloaded the xml form from our project page. After opening it in Excel I literally only modify text (such as, 5 becomes 50). I then try to upload the new saved file as a new form, but I get this error message:
"Required parameter formID missing."
RC16.xml (856.0 KB)

2. What steps can we take to reproduce this issue?
I attach the revised form that I can't upload.

3. What have you tried to fix the issue?

I have tried to open the xml original file with a text editor. However, it's nearly impossible to work with it.

4. Upload any forms or screenshots you can share publicly below.

I think you probably need to re-download your XLSForm spreadsheet form - from wherever you got it - as an RC16.xlsx file, and not try to export it as XML. Although this is XML, it is certainly not an XForm XML file definition that ODK expects, which is probably why you are getting strange errors.

<?xml version="1.0"?>
<?mso-application progid="Excel.Sheet"?>
<Workbook xmlns="urn:schemas-microsoft-com:office:spreadsheet"
 <DocumentProperties xmlns="urn:schemas-microsoft-com:office:office">

Update: I managed to modify the file and upload it successfully by working on the form with the text editor. But this is clearly suboptimal because it doesn't allow me to make any structural modifications to the form.

Thank you, but the only option given on the odk server is to download the file as xml.

Do you have the original form that was prepared for you (prior to upload into Central preferably, to eliminate variables...)