We had the ‘ready to download’ yesterday and it disappeared once on WiFi. It came back about ten minutes later and the 3 downloaded it and then presented the usual ‘software available’ notification at that point and I ‘approved’ it on the app.
I would recommend essentially ignoring it until the car is ready to install it. If you need to supply WiFi, then that needs to be done of course but there’s no way to ‘help’ it once the car is on WiFi. And once it’s downloaded, you no longer need wifi.