Any how to clear out the previous list of users who had been unsubscribed from my account ?
There is not a great bulk option for this unless you are using the account-wide Email Lists:
https://help.surveygizmo.com/help/article/link/email-lists (you may want to explore this option as it allows you to bulk unsubscribe contacts via upload)
You could always download a contact list from any specific email campaign via the “Export contacts with send status” option on the Contact tab.
This will give you a file with contact status for each contact in that specific campaign, but it sounds like it’s not exactly what you are looking for.
SurveyGizmo does track unsubscribed contacts across your account, so once someone has unsubscribed from one of your surveys, they will be unsubscribed from any future surveys (should you add them again).
I hope some of this is helpful