Simply use the command Records > Replace Field Contents.
go first record
Go Field you want the number in then
use ReplaceFieldContents step and choose Replace with serial numbers:
Jodie, do you need an actual number field for some reason?
If not, you can place a "symbol" on the layout that is:
This will change with each find, but will still be sequential 1- n (number of records), on the layout (and when printed).
Go to Layout mode, select "Insert" menu, select "Other Symbol..." and choose (or just type the value on the layout). You may notice that many of the "Get()" functions are available this way.
You may also notice that just above the "Other Symbol..." is the "Record Number Symbol" and is the quick way to get the same value! I showed you the "Other..." to let you know about the many different things in this menu.