Not sure if the last post will depict the image properly.
So:
Cell A1 (User Input): 268268-12345
Cell C1 (Calculated): =MOD(10-(MOD(((MID(A1,1,1)+MID(A1,3,1)+MID(A1,5,1)+MID(A1,8,1)+MID(A1,10,1)+MID(A1,12,1))*3)+(MID(A1,2,1)+MID(A1,4,1)+MID(A1,6,1)+MID(A1,9,1)+MID(A1,11,1)),10)),10)
Cell E1 (Calculated): =REPLACE(A1,7,1,"")&C1