All sorted. I took it to my LBS who updated the corrupt firmware via the Shimano portal. HOWEVER there was still one part of the firmware that they couldn’t fix. Came up with an error code 34 - however because the system was turned on I was able to connect via the app and successfully install the firmware over the corrupt patch. Messy but got there in the end.
Strange how the Shimano portal connected by hardware couldn’t solve it but the app could. Ah well.