Convert A4 InDesign letterhead to Microsoft Word template

We need help turning the attached PDF Letterhead (designed in Adobe InDesign on a Mac, and approved by our client) into a robust, editable Word Template (including continuation sheet) for our PC-user client.

When we've created Word templates before (using our Mac version of Word), thing 'break' once used on a PC :(

NB The office phone number also needs to change

Here's our collected InDesign A/W in case you need the fonts, links etc too...
https://www.dropbox.com/scl/fo/jf0h0afe3sex4mpv1hkyr/ALCu1Bqqq6obAXtjU4Lx4is?rlkey=o7guh1zq4qb60k2ovzj3f0im2&st=dsqvps1y&dl=0

Thanks! Jen Howell