Well, first of all, as the data has been decoded using the wrong encoding, it's likely that some of the characters are impossible to recover. It looks like it's UTF-8 data that incorrectly decoded using an 8-bit encoding.
There is no built in method to recover data like this, because it's not something that you normally do. There is no reliable way to decode the data, because it's already broken.
What you can try, is to encode the data, and decode it using the wrong encoding again, just the other way around:
byte[] data = Encoding.Default.GetBytes(input);
string output = Encoding.UTF8.GetString(data);
The Encoding.Default
uses the current ANSI encoding for your system. You can try some different encodings there and see which one gives the best result.