I'm on it American spoken language informal
It's the common phrase in spoken languague of native speakers, its more formal form is ' I'm working on it'
"Have you all submitted your working plans for next week?"."I'm working on it. I'll be finishing right after my shift.
Someone is on the process of doing something but not yet finished
"Is anybody home? You have a letter"."Hold a second, I'm on it right now"
"Get all households done then go wherever you like"."Look! I'm on it mom"
Used as a promise of a voluntary action, done for the benefit of others to glorify one's self-image
A: "This dude snore too loudly that I can't focus on" B:" Don't worry. I'm on it"
The princess: "Help me, Prince" The Prince: "I'm on it"
This phrase is actually come from the American's manner of rush when omitting 'working' from the whole sentence " I am working on it".
The inexplicable or concealed place or state indicates the afterlife.
I'm very sorry for your dad. He's beyond the veil.