What do you mean by “TAR CVF”?
Is this just “tar” command with “cvf” switches (that’s all I have been able to google)?
If so, tar switch “c” stands for “create”, extraction is made by switch “x”… :
tar xf /dev/rt0 (or whatever the tape device is)
“v” stands for verbose and is most useful for cheking the files in archive ( tar tvf /dev/… – where “t” stands for “test”)
And finally, if the archive creator is not tar, all chances are you’ll be not able to read those archives.