Ok. So, if συζωοποιέω is the infinitive, συνεζωοποίησεν would be the present perfect?
Is that correct?
συζωοποιέω is not an infinitive.
A verb is always entered into a dictionary under its first principal part. In English, the first principal part of a verb is the bare verb, e.g. "bring," "lose," "love," etc. In Greek, the first principal part is the first person singular present active indicative, so "I bring," "I lose," "I love," etc. So your dictionary lists the first principal part of Paul's συνεζωοποίησεν as συζωοποιέω, which is, as I mentioned above, the first person singular, present active indicative ("I make alive with").
Many dictionaries phrase definitions (sloppily) as infinitives: so in your dictionary (under συζωοποιέω), instead of the more accurate "I make alive," you find "to make alive."
Finally, συνεζωοποίησεν is simple past, despite the fact that the King James version translates it loosely as a present perfect.