Isn't there a burning bush in your vicinity?

The problem is that fairly high temperatures are needed, well above what a
lighter or hair dryer put out. Lighters, in particular, will burn the tubing
before shrinking it.

One workable solution is to use a hair dryer, and block the inlets with a
sock. This causes the outlet temperature to rise to the "shrinking" point.
There's a catch, though... The hair dryer will "overheat" (natch -- that's
the idea) and shut off. If the dryer doesn't have a resettable fuse, you
won't be able to use the dryer again.

A few years ago I bought an inexpensive heat gun, which worked well. A bit
of scrounging might turn one up.