So basically let the heat melt the plastic so the sets can settle in. The URL doesn't to the sets isn't available anymore btw.* Use the tip of the soldering iron to insert 4 heat sets into the top of the Pi mount, 4 more heat sets into the top of the TS board mount, 4 more into the panel mount screw receptacles on the right back mount, and 4 more into the left back mount.
Edit: yes, getting some from AliExpress