  Using the Belle data on the decay $\Upsilon(10860)\to
\Upsilon(1S)f_0(980)\to\Upsilon(1S)\pi^+\pi^-$, we estimate the fraction of the
process $\Upsilon(10860)\to\Upsilon(1S)f_0(980)\to \Upsilon(1S)\eta\pi^0$,
caused by the mixing of $a^0_0(980)$ and $f_0(980)$ resonances that breaks the
isotopic invariance due to the $K^+$ and $K^0$ meson mass difference. With an
instantaneous luminosity of $8\times10^{35}$ cm$^2\cdot$\,s$^{-1}$ at the
SuperKEKB collider, one can collect with the Belle II detector about a hundred
$\Upsilon(10860)\to\Upsilon(1S)\eta\pi^0$ events in the narrow region of the
$\eta\pi^0$ invariant mass near the $K\bar K$ thresholds in a time roughly
spent on the present Belle experiment.
