I switched from Humalog to Fiasp reason being Humalog was not "fast enough" for me.
Fiasp has been an improvement but ultimately however you plan not one of them seem to be quick enough!
There are multiple threads on the same issue.
Delete the app - go you your profile in the app store - find your list of previous apps download and reinstall from there.
When is asks you to register just skip that - you can sign in later.
All the previous data on the phone will be lost but if you...
Delete the app - then go to appstore - hit your profile and then you can reinstall from your previously purchased apps.
You will lose the data on the phone but if you are syncing to libreview it will still be there. Your existing sensor will still work