On the start tab, in the ability scores section, there is a column called "Magic Modifier"
In the cell for Strength (AP18), paste the following formula:
=IF(StartEquipmentWornHands="Gauntlets of Ogre Power",MAX(0,19-SUM(T18:AO18,H18,N18,Q18)),"")
Edit:
Checks for the exact text in the item...