Fixing tear in insulated HVAC duct?
Get a flex duct connector like is used to join two sections of flex together.
Cut completely through at the tear.
Fit the union into the inner sleeve.
Tape inner sleeve to connector.
Pull insulation back over the joint and tape well with duct tape.
If you want to insure it not pulling apart screw through duct tape with sheet metal screws around both sides into the connector.
Another method very similar uses big zip ties to secure the insulation and vapor barrier. And screws and tape to secure inner sleeve to connector
This video shows it very well.