This is going to be fun.
You're weak on AI2 and I'm weak on BLE.
I see there's new functionality on Advertisements in BLE, so that further complicates the discovery and connection workflow (which I don't have at my fingertips, and don't see at MIT App Inventor + IOT)
Could you point us to the web page for your particular device, in case that will help?
Also, I see upcoming problems for your List Pickers 2-4 (awful names, please rename them)
when you load them in
via ElementsFromString, which expects comma delimited single dimension lists.
The tooltips for DeviceServices and DeviceCharacteristics say those will return 2 dimension tables with 2 and 4 columns respectively. AI2's default list to text coercions can't flatten that. You must do it in a loop using list blocks, and load into the Elements value.
I can post samples if you want, but first read up on How to Work With Lists at