GmailAPI for sending mail

Hi,

I am trying to create a GPT lets call it Test GPT. At the end I want it to send an email to the user with regards to the conversation.
I have manage to set up the gmail API in a way that the mail goes to the user from the user itself after OAuth authentication with the Gmail API. I want to change it in a way such that the mail goes from a standard email id like testgpt@gmail.com to this user. So in this case the user should not get the oauth authentication page as it is not required.
Any tips on how to do this.