I was fetching the chromium, using
fetch chromium
and unluckily my internet went off . So i pressed ctrl+c to end the fetching process then, assuming i could start it all over again later when internet comes.
As the internet came, I wrote fetch chromium again and it said
Will using gclient sync solve the problem itself, or is there a way to delete the previous incomplete fetch and start it all over again? If yes, then how?

You can try resuming the fetch with
gclient sync, but AFAIK that is not officially supported for incomplete fetches. I have done this successfully in the past, but it may not work for you.fetchorgclient syncwill take a while, possibly a very long time, as the documentation indicates: