The "Form name" shown on the form dashboard can't be edited from the dashboard. Edit it in the Design Editor instead.
How to change a form name
Open the Design Editor.
Select the form.
Open the [Form] tab in the right panel. If the right panel is closed, open it.
Edit the [Form name].
Note: The following characters can't be used in a form name:%#?/.If you edited a site that's already published, click [Publish] in the top right to open the publish panel, then update your site to apply the changes.
Things to know when changing a form name
On the form dashboard, responses are grouped by form name. Once you change the "Form name," any responses submitted after the change will be grouped under the new name.
Example: If you change the form name from "form 1" to "form 2":
・Responses submitted after the change will be grouped under "form 2."
・Responses submitted before the change will remain grouped under "form 1."