its not an HM anymore you have to find it.
In Pokemon Platinum, Flash is a TM.
at the city of the Pokemon league
you get it from a gy
you get the HM Flash after beating the electric gym leader, if i recall correctly
There is no "HM" mean look.
The HM Whirlpool is not obtainable in Pokemon Platinum, for there is no use for it during gameplay.
Dig is not a HM in Pokemon Platinum but a TM, it can be found in the ruin maniacs cave.
Flash lost its HM status and became TM70 in Diamond, Pearl and Platinum.
You find the HM for Flash in Granite Cave in Dewford, talk to that person by the entrance and he gives you it.
in a Pokemon center
In the Generation V games (Black, White, et cetera) Flash is not an HM. To find it (as TM70) go to Castelia City. down one of the streets (the narrow one with dumpsters) you will find a man behind a dumpster. talk to him to receive TM70 Flash.
Select the Hm hit use and select Pokemon