Change Content of CustomXML in Word on a website

I have the following issue.

I offer Word templates to my customers.

These templates contain controls that you can then fill in. However, some elements are repeated in the document and also placeholders, such as the sender name, tax number, etc. are always the same.

That's why I linked the controls to an XML file. Now I also manage that the elements change everywhere, because I just linked the controls. I had now tried to create a new XML file with their personal data and to exchange this same data with the templates already in advance.

The whole thing can be solved manually super easy. However, since my customers are not technically versed, I want to solve this programmatically.

The manual procedure would be as follows:

1. download Word file
2. download custom personal XML file "Customer-XYZ.xml"
3. convert Word file to a ZIP file
4. open zip file
5. in the folder "CustomXml" is a file named "item1.xml"
6. write content of "customer-XYZ.xml" into the file "item1.xml"
7. save zip file
8. convert zip file back to word file

How would you guys programm this procedure onto a web-page?

Thanks a lot so far!!