How do you specifically find iron on Minecraft PE?

Iron occurs only around from bedrock to slightly above sea level (layers 1-63). However, almost all of the iron ore will be underground. It composes approximately 1.3% of all blocks on layers 5-40, tapering off above that. On average, there are about 77 iron ores per chunk. Due to being extremely common, iron veins are frequently seen at the boundaries of any hollow space such as caves and lava lakes, but they are no more common there than in any other volume of stone. Veins can vary in size, but the most common size is 2x2x2. Iron always comes in veins of 4 to 10 unless dirt, gravel, a cave, or another ore replaced some. Each block in the vein which otherwise would be stone has a random chance of being iron ore instead.

Minecraft Iron On

There is no SPECIFIC place for iron.Just looking around underground helps,I'd say dig a good 8-20 blocks under and start digging around.Who knows?You might find diamond too.

Did you look under that rock over there?