Either Automatic Record Numbering or Sequential Numbers

See also Sequential Annual Coding

Use a Number field instead of an AutoNumber then you can increment the numbers in your VBA.

Sequential Numbers

Thank you. :)

My data won't be entered via a form but will be imported from an Excel file. How can I change the code to accommodate this?

Put the sequential numbers on your Excel sheet first before importing it to Access.  That would be easier to do.  Just add a column on the Excel sheet and fill it with 1, 2, 3, etc.  Excel has a fast way to fill cells with a sequence of numbers too.

Thanks Kevin. I'm trying to avoid making any changes to the Excel file before importing it into Access so it's easier for other users. I'm hoping there is a way to do this with VBA.

Hi Justine, you can make a copy of the Excel file and only modify that copy.  

If you want to do it in Access, you need to use VBA to run a "Recordset loop" to go through every record and add a counter to each.  It would be much easier to add counters in Excel instead.

The videos suggested to you earlier are only for setting up counters for future data entry, not for existing data which is what you have.