I ha actually already installed Assistant 2 (I forgot about that). It won’t let me connect to my Mavic Air.
However, I persevered and look to have a solution. I found an older version of Assistant 2 on the DJI site (2018, rather than the current 2020 version). I uninstalled the newr version and installed the older version. I can at last connect to my Mavic Air and it appears to be updating the firmware 