Short answer, epoxy.
So something like araldite should do the trick?
I'm finding it difficult to find any technical data on these "consumer" products where more effort is put into selecting the right hand models than presenting specifications
Not familiar with the brand.
But if you take a look at the guide and video link, you'll notice the epoxy is applied after the trace section has been replaced and soldered, so it's not even exposed to heat at all from the iron (= non-issue, thus opening up the ability to use whatever you can find locally/off the shelf).
Good quality stuff should be available at a local hobby store that sells R/C cars and planes for example (cures hard rather than soft).
I'm assuming the broken trace is really close to the pad, which is why you're concerned. I get this, but realistically, unless it's a part that has a large thermal mass, on a ground/power plane or both, the amount of time the iron will be on the joint at some potential later date (fix as per the guide first, then some later repair), a common, good quality, off the self brand should survive (talking a couple of seconds here).
Not sure on brands available to you, but if you're still concerned, a temp specification you'll want to look for is 260C/500F (i.e. test data, if available, should show it can survive for ~ 1 hour/60 min. at this temp without degradation). Up it to 288C/550F, and the test data will drop to ~ 20 min. BTW, this is the type of epoxy ratings you'd find used in standard FR4 PCB material (no need to look for higher, which does exist).