First do nothing until the first amended return has fully processed ... then simply log back in and start the amendment process again ... when you look at the 1040X column A should have the first amendment's figures.
It is taking months for the IRS to process amended returns. So your first amended return may very well still be sitting in a pile of unopened mail. The IRS is working on opening over 11 million pieces if mail that piled up in trailers during the pandemic. The "normal" four months to process an amended return is taking much longer. If you mail or send in a second amended return before they finish processing the first one, you could create a lot more confusion and delay and wait for a VERY long time. Wait. You have three years to file an amended return--so you have plenty of time.
When the IRS finally opens its mail and begins to process mailed returns you can check the status on the IRS site.