audio transformer doubt

im trying to do this project 9 Ways to Transmit Audio With a Laser Pen - wikiHow

but im unsure of the transformer to use. i went to the store n asked 4 "an audio output transformer". the dealer said "what transformer?". n he gave me a 6-0-6 volt transformer, said that he does not have other transformers.

well, i used my multimeter to test the resistance.
in that transformer, on the side where 2 wires r coming, its 1.7kohm

on the other side where 3 wires r coming, if i connect the 2 outside yellow wires to the multimeter, it shows 14 ohm.

if i connect the middle green wire to either of the yellow wires, the resistance is 7.4 ohm.

now, how do i use this transformer in the project at 9 Ways to Transmit Audio With a Laser Pen - wikiHow ?