Back up first.
Then go to your define fields and change your number field to calculation. It will warn you but it is okay because you have no data in that field. Then in the calculation box, put only a single 0. At bottom, it will default number but verify that it is number.
You will not need to do anything in Storage Options. Your calculation (which was number field) should default to allow indexing but you might check it for reassurance ... it should be checked to 'automatically create index as needed.' Say OK to save the change then say OK to exit Define Fields. This will turn all your records to a 0 on that field.
Now go back in and change the field back to standard number. Your records will hold that value until you change it manually (or via script) . :smileyhappy:
You can also show all records and then use Replace Field Contents (place your cursor in field if manual change or script it) and just put a 0 in the calculation dialog. No method that mass replaces data is safe in multi-user mode unless using a scripted loop with error trapping so do it when unserved or when no users are in the system.