- place insert at the hole location in plastic,
- Heat up Iron solder to 250- 350 deg C
- Touch the insert from top and heat it up with soldering iron (or insert installing iron).
- Gently push down on insert, try to guide it to be vertical when it will level up with plastic!!
- Leave the plastic part to cool down.
- Remove any access plastic with sharp knife.
Screw in screw to clean out any more plastic from threads
You are Done :-)
Long version - see: • How To Install Heat Se...