Test Flight Minimum Version is iOS 13 - How can I test my app on devices that don't support iOS 13?

I have several devices in my test pool that cannot install iOS13.0 and are capped at iOS 12.5.5.

We still support these devices, but without Test flight, I no longer have the ability to deploy builds to these devices.

Does anyone know how to install an .ipa file directly to an iOS device sans building from Xcode?

My team needs to be able to install builds on these older devices but we are blocked.

Any info would be welcome.