Formula to subtract 1 from month 1

I imported some data into Excel, however the dates are incorrect, so I would like to roll back the date by 1 month. I.E. if the field says 10/13/2003, I would like to change it to 09/13/03. If there is a way to do so, is it possible to also correct the year if you change 01/13/04 to the previous month, which is supposed to be 12/13/03?

Below is a sample of the input:

Event Date Payment Interest Principal Balance
Loan 10-02-2003 17,754.81
1 11-02-2003 301.85 102.09 199.76 17,555.05
2 12-02-2003 301.85 100.94 200.91 17,354.14
2003 Total 603.70 203.03 400.67

3 01-02-2004 301.85 99.79 202.06 17,152.08
4 02-02-2004 301.85 98.62 203.23 16,948.85
5 03-02-2004 301.85 97.46 204.39 16,744.46
6 04-02-2004 301.85 96.28 205.57 16,538.89
7 05-02-2004 301.85 95.10 206.75 16,332.14
8 06-02-2004 301.85 93.91 207.94 16,124.20
9 07-02-2004 301.85 92.71 209.14 15,915.06
10 08-02-2004 301.85 91.51 210.34 15,704.72
11 09-02-2004 301.85 90.30 211.55 15,493.17
12 10-02-2004 301.85 89.09 212.76 15,280.41
13 11-02-2004 301.85 87.86 213.99 15,066.42
14 12-02-2004 301.85 86.63 215.22 14,851.20
2004 Total 3,622.20 1,119.26 2,502.94

Any help on resolving this issue would be greatly appreciated.

Thanks,

John