Quick and simple for now.
Change this line
Code:
sh2.Cells(sh2.Columns(3).Find(a, , , 1).Row, 7).Value = sh1.Cells(i, 5).Offset(, -1).Value
to this
Code:
sh2.Cells(sh2.Columns(3).Find(a, , , 1).Row, 7).Value = sh2.Cells(sh2.Columns(3).Find(a, , , 1).Row, 7).Value + sh1.Cells(i, 5).Offset(, -1).Value