Well in an all-encompassing answer that doesn't ask for more answers from the questioner, if you've got the beastly form that looks like a shark (and is pinkish-purple) then go towards the entrance to Mithalas City and head straight up using your new form to pass the strong current at the top. If you havn't gotten that yet, head back to open waters (the main area from which you accessed the Kelp Forest) and head directly RIGHT. You will find Mithalas City, it's rather unmistakable there's broken pod buildings everywhere.
And if by some chance you're already IN Mithalas City head to the cathedral on the far right of that.
And if you're already THERE we're gonna need specifics before we can assist further.