The panel on the front is based on sort files. You would need to rebuild the sort files if you feel the information is not correct.  If the quantity on hand does not match what is in the system then you have to do either an adjustment in Inventory transaction entry or do a physical count.

With Sage 100 you never edit QoH directly.  Instead, you post appropriate transactions (receipts, issues, sales, transfers, adjustments...) to change this value.

And in general, Inquiry screens are for viewing only.  Any edits related to item settings would be made through Item Maintenance.