I am sorry to hear that you are experiencing issues with lost premium shipping eligibility.
You will need to submit a Plan of Action if you would like to appeal, otherwise, you should be able to offer the service again automatically after a few weeks.
According to Amazon, “To restore eligibility for Premium Shipping Options, please submit a Plan of Action by replying to this email or writing to [[email protected]].
To offer Premium Shipping options, sellers are required to:
** Have sold on Amazon for 90 days or more*
** Ship ten or more orders in the last 30 days*
** Maintain an on-time delivery rate of 97% or greater for all Premium Shipping option orders*
** Maintain a valid tracking rate of 100% for all Premium Shipping option orders*
** Maintain a cancellation rate of 0.5% or less for all Premium Shipping option orders”*
However, I do have a handy Plan of Action template which you can use: