The Lorentz shift of electrons in a magnetic field is taken into account with simulating the response of a GEM detector for the BM@N experiment. Dependences of the determined coordinate x on the track angle, the values of the Lorentz shift of electrons and its dispersion for the gas mixture ArC4H10 were obtained. The momentum resolution was obtained as a function of the momentum for the deuteron-carbon (dC) process, and the invariant mass of the Λ-hyperon was determined. The obtained results are close to the first results of experimental data collected in the technical run in interactions of the deuteron beam of 4 AGeV with different targets.