I have a document library set to automatically increment a document number and
it works great thru all my testing. Each time a document is added, the library
assigns the next sequential number to it. I used calculated fields and a
custom-workflow for it. This is how I did it:

First create a new field called FormId, then in SharePoint Designer create a
workflow to run when a new item is created, leave the Condition field blank and
under Action, select Update Item, FormId = (current item) ID. This workflow
will now copy the ID field to the FormID field.
Next, change both your calculated fields to run against the FormId field instead
of the ID field:
ID Set
=IF(FormID<10,"000",IF(AND(FormID<100,FormID>=10),"00",IF(AND(FormID<1000,FormID\
>=100),"0","")))
Incremental Form ID ="P"&ID Set&FormID
This will result in the assigning an incremental number to a new item when it is
created.

My problem is that now that I am done with testing, I want to start loading in
real documents, but I want to start over again and have the first document
be 1 . How do I do this?