97 Chevy blazer had an complete tune up . BUT my check engine light came right back on again reading misfire what else could it be

I have a 97' Chevy Blazer. My check
Engine light came on bout a week are so
ago. But during that time, during that
week I'd went to auto parts store were
they said I'd a misfire. So I'd gotten a
complete tune up, change plugs, wires
ignition corals, everything replaced. So
after completing my tune up my check
engine light finally went off, until I'd rode
down the road just to notice my check
engine light came right back on again,
this time flashing. What does that mean?