I found the power button on eBay. I would assume that you would just push the power button into place with moderate amounts of force and it would just “click” in. If that doesn’t work, you seem to have a game plan of what to do without a power button and I would personally just stick to that if all else fails .
https://www.ebay.com/itm/OEM-VERIZON-ELLIPSIS-8-QTAQZ3-8-POWER-BUTTON-REPLACEMENT-/361405567942