Channel estimation in high-mobility environments presents a significant challenge for advanced mobile communication systems, including 5G and beyond. In this study, we address the challenge of channel estimation in high-mobility scenarios for 5G and beyond, where orthogonal time frequency space (OTFS) modulation outperforms orthogonal frequency division multiplexing (OFDM). To enhance spectral efficiency, we integrate superimposed pilots combined with index modulation. The proposed method is an iterative algorithm for OTFS with dual-mode index modulation (OTFS-DM-IM) systems that performs channel estimation and symbol detection using a superimposed pilot pattern. This algorithm alternates between data detection using LMMSE and data-aided channel estimation. Simulation results show that the proposed algorithm achieves a good balance between spectral efficiency, BER performance, and computational complexity.