Both XSD and XML are text files that contain variations of XML documents, you probably cannot convert one to each other, but you can both edit using a text editor. Some online services might also help, but what they usually do is to export an XML sample from a XSD file.
Convert XML schema description to XML document.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert xsd to xml on Windows
XML integrated development environment
Convert from xsd file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.