If the component is external and you don’t have access to the original file, you may not be able to navigate there. If that’s not the case and you are sure that the component is/was local in the current file, you may have found a bug and should send a report and a link to the file to Figma support team via the support request form or support@figma.com.
OK. I just filed a bug needlessly, so this reply might help someone like me… Right click on your Child component and select: Main component > Go to main component (or Restore main component if you were stupid enough to hide it like I did. Lol)