It means deleting the variable and re-creating it. You can use the approach Pinok84 suggests, but you can also try to narrow down which one it is.
Your text editor may just say that the file is a binary, in which case a hex editor may help you find the “NoneNone”, in context to the variable name or type. It can be a bit tricky to interpret this, as uasset files aren’t super human readable. But generally you can look for the decoded text above/before the NoneNone. There might be some unreadable data in between, but you may recognize things like “Default”, “KismetSchema”, and eventually — hopefully — a variable name from your project.