File conversion--lock out

Created a workbook in ver 3.6.2 on an old MacBook Pro (mid 2010) running El Capitan. The MacBook Pro can not update OS to newer versions. I opened the file using Numbers ver 5.1 (6569) on my iPad without making any edits and now I'm locked out when I try to access it using my MacBook Pro. The error message tells me its time to upgrade Numbers to access the file--but I can't. Is there a way to recover the file for use in an older version?

Many thanks.