How I can give an existing jotform created by me to another new user?

If you wish to transfer the account to a new user, we can transfer all your forms to that account. Just open a new thread requesting the form transfer and provide the username of the new account so that we can move all your forms. Once we move the ownership of the forms will be changed to that account.

Alternatively, you can change the ownership of your account. Just give your login credentials to the new user and you can change the username and email address of this account in the profile page.

Here is the guide: How-to-Change-the-Username