You cannot enter a beginning balance for the AFE codes. The only way you can get around this is to mark the expenses that you already used as AFE expense. This would show all of those expenses on the AFE then and it would pick up the previous amounts.
The only other option would be to enter all of these expenses again with all the same info except the amount will be a negative. This will cancel out all of the previous expenses entered. Then enter the expense again under the correct expense code. The amounts will cancel each other out but they will then report correctly.
Return to the AFE Module