A family of Microsoft relational database management systems designed for ease of use.
Access is a database and copy/paste operations seldom make sense in a database in contexts like this.
There are ways to update values for multiple records at a time, but copy/paste is a blunt force instrument not well suited to the goal. In this case, it appears that you do want to update everything in the Item_PO# field, but that's the exception.
Instead, you use Update Queries that selectively apply the changes to only those records you need to update.
In this case, it sounds like you want to update every record in the recordset to the same default value. That can be done like this:
UPDATE YourTableNameGoesHere
SET Item_PO# = .01;
A more common requirement is to selectively modify values in some records, but not others. In such cases, the Update queries might look like this:
UPDATE YourTableNameGoesHere
SET Item_PO# = .01
WHERE District = "K";