Write number of atoms in each element.
Left Hand Side has Sn = 1, O = 2, H = 2
Right Hand Side has Sn = 1, H = 2, O = 1
So, Oxygen atoms are not balanced at the products side.
Add 2 infornt of H2O and 2 before H2.
SnO2 + 2H2 → Sn + 2H2O
Again, check the number of atoms in each element
Left Hand Side has Sn = 1, O = 2, H = 2x2 = 4
Right Hand Side has Sn = 1, H = 2x2 = 4, O = 1x2 = 2
The equation is balanced.