You can bulk upload coins to users via csv.  First, select the section you are importing the coins to, then click on Import coins from csv:

The CSV MUST exactly contain the columns 'email' and 'coins' as users will be identified by their email address in the selected section.  It does not matter if there are other columns on the sheet.  

Simply choose the CSV file and click on "Import Coins":

Pro Tip:

If you want to import coins to the existing users on the dashboard, go to the users listing page, then click "Download CSV".  This sheet will have the user's email addresses and current coin count.  Simply edit the "coins" column as needed, save the file, then use it in the Import Coins tool.