I assume you are using OOo Calc or LibreOffice Calc?
Check out the "Left" and "Right" read commands. You can make Column B the left "x" number of characters of Column A and Column C as the right number of characters of Column A. I think there is even a way to subtract a string from another string ("ABC" - "A" = "BC"), but I may be wrong.
NOW BACK UP YOUR WORK TO ANOTHER FILE.
Then in columns D and E, copy columns B and C as absolute values, NOT as references. Finally, blow away columns A, B, and C. You will be left with the two columns of data you want.
I just checked it out in OOo. If cell A1 contains (without quotes) "abcdefghijk" as text and in cell B1 you use the formula (without quotes) "=LEFT(A1; 5)", abcde will appear in cell B1. Just remember that that is a reference value, so you have to copy it to another place as an absolute value.