Use APKPure App
Get Bluetooth GPS Provider old version APK for Android
This tool allows you use your external Bluetooth GPS to send its data to any GPS application that can select the provider.
"Mock Locations" have to be enabled.
Please note that this will only work if your GPS application is able to select the provider. Most will select the default "internal" and they won't be able to use this tool.
My own "Turbo GPS" supports choosing the provider.