After my 2019 return was accepted I amended the return through Turbo Tax to include prepayments that I forgot to include.How do I know if the amended return was accepted.

For information on how to track the status of your amended return, please click the link below.

How do I track my amend status? - Community

You needed to wait to amend until the IRS was done processing your first return.  They will probably automatically catch that and add them in for you.  

If you think you efiled the amended return, you did not.  Amended returns don't get Accepted or Rejected.  Amended returns can only be mailed not efiled.  The amended return is only for the difference you get back or owe.  You will still get the first refund or need to pay the tax due on the first return.  They only mail checks for amended refunds.

After 3 weeks you can track it here,    https://www.irs.gov/filing/individuals/amended-returns-form-1040-x-/wheres-my-amended-return-1