Information on creating a Splashtop JSON can be found here under the installation files heading:
Navigate to your Profiles tab and click the plus sign under Available Payloads.
Select Android and then File
Name your payload, select Add/update file, specify the file path for your particular device type (\enterprise\usr\persist, \persist, or \sdcard), browse to your JSON under File, and select Save
Your file payload will now show under Available Payloads