format username:password?

[uwualex]

I'm basically trying to format the whole thing as username:password.
My hashlist looks soemthing like this:
Username:Hash 

What im trying to do is have it like so:
Username: Dehashed

How do i go on about formatting this with hashcat?

So far i have tried:
-m 0 --username --potfile-path md5.pot --show -o formatted_output.txt --outfile-format 2 original_MD5_hashes.txt

But it doesn't seem to work, it shows:
Failed to parse hashes using the 'native hashcat' format.


Any help is highly appreciated, i hope you can understand what im trying to say. English is not my first language.
Thanks!