How to correct song duration

I divided one file (8:25) into two songs. One song (4:17) is saved into the former file and the second file (4:08) is saved in the new.

In MP3TAG the lenght of the first song is shown as 8:25. How can I reset this to the correct value?
The copy into a new file with the song editor is too easy.

Who has an idea?

you have to repair the file header. Use e.g. mp3val, foobar2000 or mp3diags.