Typically readers will want to know enough about your methods to potentially do a replication, if desired. Failure to disclose enough about the methods could lead to a rejection if you are submitting it to a journal, or at least a revision requesting the missing information. Not stating how something was done can also raise some eyebrows as to the validity of the method and subsequent results if the method and/or author is unfamiliar. However, if this is a relatively common method in your field - and you personally just don't happen to know how it's done - you might get away with being more broad, as readers will know what you're referring to or be able to find other sources to inform them.
In the latter case, I've seen papers say something like, "The transformation was conducted by a member of the research team as suggested/conducted by Author et al. (2016)." They don't go into details themselves, but rather point the reader to another paper if they care to know the details. However, in order to write it up that way, you still need some idea of what was done and who might have established the method or used it in another paper. Can you reach out to the cooperator yourself and ask if they have a few minutes to discuss the method?
