We measure collective excitations of a harmonically trapped two-dimensional (2D) SU() Fermi gas of confined to a stack of layers formed by a one-dimensional optical lattice. Quadrupole and breathing modes are excited and monitored in the collisionless regime with tunable spin. We observe that the quadrupole mode frequency decreases with increasing number of spin components due to the amplification of the interaction effect by in agreement with a theoretical prediction based on 2D kinetic equations. The breathing mode frequency, however, is measured to be twice the dipole oscillation frequency regardless of . We also follow the evolution of collective excitations in the dimensional crossover from two to three dimensions and characterize the damping rate of quadrupole and breathing modes for tunable SU() fermions, both of which reveal the enhanced interparticle collisions for larger spin. Our result paves the way to investigate the collective property of 2D SU() Fermi liquid with enlarged spin.