So, this is just a matter of using the appropriate (assume windows?) File I/O header and code.
Its fairly low level/basic. And you should be able to add it within your header without any issue so as to make custom calls to it.
Instead of using Unreal methods for it, just use the native ones.
Writing the stream to the file should be trivial since I know for a fact there is an engine function that makes the stream accessible…