It is something that does not look like either utf-8 or iso-8859-1. It might be anything else. It may even not be a text at all. This type is kind of fall-back description for anything that does not contain zero bytes.
Even if it actually is a text file (the extension suggests it might be), there is unfortunately no automatic way to find out the encoding, because most encodings have the same range of valid codes. Utf-8 can be told apart with very high confidence, but beyond that it requires manual checking.
First you have to find out what language the file is in to get some idea what is correct content and what is garbled content and to have a list of possible encodings. Because there are zillions of encodings, but only few were used for any particular language.
Than you need to try converting the file from each possible encoding and for each conversion that succeeds technically (which unfortunately will be most of them) view the result and check whether it is correct or not.
A spell-checker might help you with the review, since incorrect conversions will lead to more spell checker errors.
For the conversion, you can use
iconv(1), which is installed from libc package on GNU/Linux or
recode has more options and better error handling.