I downloaded this and extracted nano from the url below via midnightcommander. In windows, 7-zip can unzip this rpm file. Copy the binary nano-file found in ./usr/bin/ directory onto your esxi 6.5. Probably put it in directory where you got other executables, like in /bin or /usr/bin.
For windows users, the winscp client is great to copy the nano into the esxi host. If you run linux, just scp the binary to your server like this: