Singing can't hear my voice on iphone earplugs

Guy's I'm a liiitle bit into music and would like to record a few song's over my iphone.
The only problem that I have is:

I would love to hear my voice over the earplug's while acapella recording.

Anyone got an idea with what kind of app or option, I can get it to work?

Thank's!!!!

Singing can't hear my voice on iphone earplugs