Upgrading from 100.3 to 105.5 on a RPI Zero

I have 100.3 running on a RPI zero. I wanted to upgrade to 105.5 but I get tjhe error: homeassistant needs python3.6 not >3.7.

I updated to 3.7 because my iOS Home Assistant app requested this. I have tried to force the use of python3.6 but not successfully. Any ideas much appreciated. I have a copy of my configuration.yaml so perhaps I should just re-install completely and then copy across my configuration? Would this work? Or should I use a RPI3 or 4? Thanks