Create a Number Field PrimaryID or whatever.
Select Options and set the field to Serial Number
Find all records, sort in the order you wish (not necessary).
Select the PrimaryID field, under Records Menu choose Replace Field Contents - Serial Number is a choice.
In Excel you could select the first cell and choose Fill > Series > increment by one and create as many records as you like.
Filemaker could do the same with a script.
This worked to perfection. Much appreciated