Connecting bluetooth

I want the user to be able to turn on the bluetooth when it off

With this extension you can enable/disable Bluetooth
http://kio4.com/appinventor/242_extension_bluetooth.htm

i use this extension in my project after i sign out and when wanted to open the project after sign in i had this massage " unable to find component ''KIO4_Bluetooth'' while loading". the project can't open any help?

Create an app with only these blocks, install it.

bluetoothextt

This works for me on Android 9.
What version of Android do you use?

the issue is i can not open the project from app inventor 2 platform after i added "KIO4 Bluetooth" extension

I have not had a problem with that extension, can you export the .aia to your PC?