The rare-earth frustrated magnets with dipole-octupole doublet trigger intense research interests due to their exotic quantum phases including spin fragmentation. The newly discovered rare-earth magnet KErSe2 is a promising realization of the dipole-octupole doublet on the triangular lattice and shows no evidence for long range magnetic order down to 0.2K. Therefore, the determination of the single ion ground state by crystal field analysis will be crucial for understanding the spin state in KErSe2. We request 2-days beamtime on MAPS for the crystal field measurement.