Pronounce the "bla" portion of blason as you would pronounce the "bla" in "blahs."
Draw the "ah" vowel sound out a little longer than you would in most English words.
Pronounce the "s" portion of "blason" the same way you pronounce the "s" sound in "sizzle."
Transition from the "s" to the "on" sound, and finish pronouncing the word as if you were saying the word "zone."
Practice saying the word over and over until it feels comfortable and natural.