When the incident solar wind He2+ and H+ distributions cross the electrostatic potential at the shock, they are decelerated differentially due to their different charge- to-mass ratios. This differential slowing will produce a He2+ ring-beam distribution immediately downstream from a quasi-perpendicular shock. In this letter, we perform one-dimensional (1D) hybrid simulations and investigate the evolution of the He2+ ring-beam distribution in magnetized plasma. The plasma is composed of three components: H+, He2+ and electrons, where H+ has a velocity distribution with large perpendicular temperature anisotropy. It is shown that both the He2+ ring-beam distribution and H+ distribution with large perpendicular temperature anisotropy can excite ion cyclotron waves with propagation direction parallel to the ambient magnetic field, and then the waves pitch-angle scatter the He2+ ions. However, only the ion cyclotron waves excited by the He2+ ring-beam distribution can transform He2+ into shell-like distribution. The results can explain the He2+ shell-like distributions downstream of the Earth's bow shock, which have already been observed with the AMPTE/CCE and ISEE spacecraft.