Does 7Zip have any connection with RAR archive? I've never heard 7-Zip tool can really extract from a corrupt RAR archive. The WinRAR tool is capable enough to repair RAR archive. It has a couple of features which you can use to repair RAR archive.
First you should try to repair RAR archive by using its built-in repair feature.
Secondly you can try to extract data from corrupt RAR archive file.
If the original source is available, it's better to download the file again. Maybe you can't extract data from the corrupt RAR archive by doing anything, not even by using a professional recovery solution. Though you can try a couple of manual tricks to repair RAR archive, but if they fail or don't work for you, you should download the file again instead of spending money on paid recovery tools.