repairs to 1993 escort wagon professionally, now engine light is on?

the engine light was never on before i had the valve gasket replaced, serpintine belt replaced, and oil changed with additive, could the additive melted away at a hose or something? some of, i mean one of the hoses is bad that i can see, a small one comming off of the fuel injekter, that thing needs to be replaced. can i make the pro fix my engine problem that he gave me?