Blinking blue indicates that the GDL39 is actively searching for a connection.
I would double check that the BT has not went wonky on the tablet. Do a full restart on the tablet, etc.
Here is other advice from the manual:
"NOTE: If having issues making a Bluetooth connection hold the power button
down for 5 seconds. The blue LED will begin blinking. Release the power
button and then press the Power button again for 5 seconds. Power cycle
the GDL 39 and retry making a Bluetooth connection. "
Step two if that does not work: Contact TeamX
g3xpert@garmin.com
Typically the flat rate repair of out of warranty aviation devices is listed on their website. Strange however that the GDL 39 does not seem to be in the list.