The other day, I opened the Camera app on Microsoft Lumia 640 which I have updated to Windows 10 and there were no Lenses pre-installed. So I clicked the link to the Store and installed a few lenses, including Microsoft Office Lens. However, when I got back to the lenses screen to use them, nothing was there. I closed the Camera app and opened it again, opened the apps I had installed and looked for an option to add them to the lenses menu, even restarted my phone. Nothing worked. The menu is still empty. What should I do to add the apps to the Lenses menu in the Camera app?
I found the answer to my own question, so I'm sharing it with others who might have a similar problem: I reset my phone in Settings -> About -> Reset phone and then updated the Windows Camera app and reinstalled the lens apps. The problem is now solved.