Okay I can't seem to find what a private key truely is, and it's purpose.
I have a private key that  is linked to a transaction that is messed up and I would like to take my money back if at all possible
how do I do so?
If that is not the purpose of the private key please explain.

I looked at the format for this, but it really doesn't fit what I did
Bitcoin Client Software and Version Number://I used blockchain.info
Operating System://
System Hardware Specs://
Description of Problem:I sent money, to myself accidentally , and it came back as "Outpoint already spent"
Any Related Addresses:Recieving adress : 1MuhTpbyfsnfS1fmNoTqyziqtLSjqgNABk
Any Related Transaction IDs: https://blockchain.info/tx/fb67bc8630afcb89d5d7267691afa1e351a1724d51185fc35990afdcc9cfff73
Screenshot of the problem:
https://gyazo.com/5d1d118117266c8653dafd7c54288e89
Log Files from the Bitcoin Client: I don't think I can get this

Please help me figure this out, as it seems I am out of $34 BTC at the moment

//Side note
I've googled all I could, nothing can really be found, other than how I was using a shitty wallet.
Now I use Exodus : 17m4VTJJg85ddPYF85DewBbwurSpPwABDT