…I’d remove the eMMC entirely, install the new M.2 SSD - then install W10 with the instructions contained in the thread below:
https://forum.chuwi.com/t/useful-larkbox-rebuild-links/15897/7
…perhaps experiment with adding the eMMC back in later as D: – some posts say the eMMC interferes, asserting control and boots to itself regardless of position.
-Rob