If the mark is an end of file and NOT end of tape then you should be able to address the tape drive multiple times through the nonrewinding interface. Then name of that interface depends on your Linux distribution. Doing this the first time should move the tape past the EOF marker. Then you should be able to read whatever data is left on the tape.
Usually the nonrewinding interface for a tape device is the same as the tape device except that it begins with the letter n. If your tape drive is /dev/rmt1 then the nonrewinding interface should be /dev/nrmt1.
So you could use the dd command to move the tape past the EOF, then read the rest of the data.
dd if=/dev/nrmt/1 of=/dev/null
Now read the rest of the data.
You should always state the Linux distribution and version that you are working with.