  T- and S-duality rules among the gauge potentials in type II supergravities
are studied. In particular, by following the approach of arXiv:1909.01335, we
determine the T- and S-duality rules for certain mixed-symmetry potentials,
which couple to supersymmetric branes with tension $T\propto g_s^{-n}$ ($n\leq
4$). Although the T-duality rules are rather intricate, we find a certain
redefinition of potentials which considerably simplifies the duality rules.
After the redefinition, potentials are identified with components of the
T-duality-covariant potentials, which have been predicted by the $E_{11}$
conjecture. We also discuss the field strengths of the mixed-symmetry
potentials.
