In order to understand the roles of metal flows in galaxy formation and evolution, we analyze our self-consistent cosmological chemo-dynamical simulation of a Milky Way like galaxy during its thin-disc phase. Our simulated galaxy disc qualitatively reproduces the variation of the dichotomy in [α/Fe]-[Fe/H] at different Galactocentric distances as derived by APOGEE-DR16, as well as the stellar age distribution in [α/Fe]-[Fe/H] from APOKASC-2. The disc grows from the inside out, with a radial gradient in the star-formation rate during the entire phase. Despite the radial dependence, we find a universal profile for the outflow-to-infall ratio independent of redshift, which indicates a self regulated formation of Milky Way like galaxies. The simulated disc undergoes two modes of gas inflows: (i) an infall of metal-poor and relatively low-[α/Fe] gas, and (ii) a radial flow where already chemically enriched gas moves inwards with an average velocity of ∼ 0.7 km/s. Moreover, we find that stellar migrations mostly happen outwards, on typical timescales of ∼ 5 Gyr. Our predicted radial metallicity gradients agree with the observations from APOGEE-DR16, and the main effect of stellar migrations is to flatten the radial metallicity profiles by 0.05 dex/kpc in the slopes. We also show that the effect of migrations can appear more important in [α/Fe] ratios than in the [Fe/H]-age relation for thin-disc stars.