How to figure out code for why check engine light is coming on in a swapped honda civic?

My friend has a Swapped 1993 Honda Civic Ex that has a 1994 Acura Integra gsr with vtec motor. His check engine light keeps coming on and he wants to know how he can check what it is, he has the equipment to check it. He just needs to know how to do it for a swap he knows how to do it in general for non swapped cars, we tried calling places but they wont tell us due to the fact they want us to come in and spend money.How to figure out code for why check engine light is coming on in a swapped honda civic?In my car that light comes on when it's due for an oil change.How to figure out code for why check engine light is coming on in a swapped honda civic?if he has a scanner he needs to connect it to the diagnostic port under the dash and read the code or buy a cheap one at parts store