If a user finds that he/she has data pre-populate in the fields of a Giving form, it is because the browser settings are remembering the information for those fields. The Giving form does not remember the data, it is the browser (Chrome, Firefox, etc.) that remembers the data and inserts it into the form.
If the user wants the data to pre-populate, make sure the settings in the browser remember the data the user is entering in the fields. Clearing browser data may remove these fields with the data stored in them.