How do I retrieve a "lost" e-mail folder from back-up drive- mac mail deleted the folder

Mac Mail. A pain. Love it and remember this issue before. I backed up this morning on my external hard drive, and do have i-cloud. FYI. II was moving messages into an e-mail folder for business folder that was a sub-folder under another, I selected the folder to re-name it, and recalled that you cannot rename a folder or all the messages disappear....that happened once...but I accidentally hit return instead of selecting another folder, and POOF, the entire sub folder is GONE.. everything I needed to access today to do my work! How can it go away without a pop up that says "are you sure you want to delete this folder"?

HELP- I see in my back-up drive that I save this morning at least, and I have i-cloud. I already went to my on-line yahoo account, and since the folders are synched, it is also gone from there too 😟 I need to access all these e-mails and reply today!! Help/.....