Make sure your top kit has a reinforced area/band.
Drill a 2mm pilot hole in the centre of the reinforced area/band. You should ideally use a pillar driller or mounted Black & Decker type, not a free hand drill. Caution should be taken bearing in mind all safety aspects including wearing goggles. If under 18 years old you should ask a competent adult to carry out the work.
Drill a 5mm hole using the pilot hole as a guide.
Carefully push in the bush until it clicks in place.
Run some resin like varnish or araldite around the outside edge of the bush with a small paint brush.
Allow to set and you are ready to go.