[Users] Reset the last email collected from a server

[claws at waghornswood.net.nz]

Hello, I recently had a hard drive problem that resulted in loosing a week
of mail. Its still on the servers not not too bad.
 How do I reset the last collected date or last email collected per account?
I have looked at folderlist.xml but nothing in there to me stands out as a
pointer for the last received email.

Thanks 
Oscar