From the Modify Serialized Items form there are two ways to add a count of serialized items to an Inventory Count:
Modify Serial Numbers Individually
Open the Modify Serialized Items form.

Under Add/Scan Serialized Item, add the item's serial number to the Serial Number field.
Note
You may only have permission to enter the number by using the scanner.
Select the Inventory Status from the drop-down list.
Click Add to add the item to the bottom of the window or click Clear to empty the fields and start over.
Repeat as needed for other items.
When all of the items have been entered, click Save.
OR
Add Serial Numbers in Bulk

Add any common starting numbers or letters for all serialized items to the Prefix field (if applicable).
Fill in the From and To fields with the starting and ending numbers.
If there are common ending numbers or letters, enter those in the Suffix field.
Click Add to populate the Serial Numbers in the bottom of the Bulk Add window.
At the confirmation prompt, double check and click OK if correct, or make changes if needed.
Click OK to close this form and populate the Modify Serialized Items form with these items.
Click Save when you're done. This populates the Inventory Count Details form.