"Owner" status of a Splashtop subscription cannot be transferred from one account to another. Instead, you would have to change the email of the "Owner" account to the desired email.
- Login to the website my.splashtop.com with the owner account.
- Hover the mouse over your email ID at the top right of the page and choose "Account Info".
- Click "change email" to change the email of the owner account.
- If you are changing the email to an already existing account in Splashtop servers, you need to delete or change the email of that account first by going to https://my.splashtop.com/account_info/ and click delete my account link on bottom right of page. See this article for step by step guide: https://support-splashtopbusiness.splashtop.com/hc/en-us/articles/213193643-How-to-change-my-email-address-or-password-Or-delete-my-account-