HERE IS THE WAY TO DO IT!
1. Ensure that the tongue on the bottom of the filter holder sits nicely in the socket at the bottom of the kettle.
2. Fill the kettle with water and boil the kettle - it doesn't matter if the filter holder flops away as long as the tongue is still located in its socket.
3. Empty the kettle of the boiling water and using oven gloves, push the filter holder down and under the lip of the kettle.
NOTE: the hot water softens the plastic enough to make the process easy. It is almost impossible to insert the filter holder into place in its COLD condition.
YanP, September 2017