Unfortunately, .eeg is not a standardized format, many manufactures use that extension, for different format files. As per this previous post:
As you have .eeg and .ptn files, try to read them as "EEG: Nihon Kohden”
If that does not work, try with the other formats that are also .eeg:
https://neuroimage.usc.edu/brainstorm/#Supported_file_formats