If you're comfortable working at the file level, you can still access it. - click help.troubleshootinginformation - scroll down to 'profile folder' and click 'open profile' - exit thunderbird - if the folder was in POP or local folders, click the Mail folder and then possibly the Local Folders folder and the renamed file should appear. Rename it back to what it was, delete the associated msf file, and then restart thunderbird and see if it appears.

Thanks for your reply! The issues got resolved. The renamed folders were hidden, what I did was clicked on my mail account and selected subscribe option where all my folders (including the renamed ones) were shown, there I selected the folders to be shown in inbox and saved, and they're visible in my inbox now.