It should be possible to parse .json files to .yaml files either using dedicated JSON parser utility or perhaps with the help of some of online based JSON converters and parsers.
Some of the most popular include Code Beauty or JSON Formatter and both can be used to convert, format, beautify, mimic or compact json files and can also be used for the purposes of json to yaml conversion.
However, it may not be perfect in all cases, especially if there are some kind of uncommon object that not all interpreters may handle flawlessly.