You can change the default form layout for Note enitty in timeline component.
1. Go to make.powerapps.com and get in the edit page of your form.
2. Select the timeline component on form.
3. Find "Record settings" in the right panel and target "Notes" under REcord settings, Click the "Default form".
4. Change the "Data field" to Created By.
5. Publish all the changes.
Here is a picture show about the steps:

Result screenshot after published changs:
