Part of improving his cardio is just going to be keeping cool and fighting smarter. Conor openly admitted he panicked against Nate, and that his tactics had not been too clever.
Now he knows that unlike, say, Anderson Silva, Conor's division-crossing power is a myth, Conor won't lean on it so hard that it depletes him. He has the technique and timing to fight longer while still landing more than his opponent does, so should still be able to find ways to win over more rounds as long as he can keep his cool.
The real question may be how much better Nate's defensive and offensive striking will be from the get go with a proper camp to tune up his timing, range and rhythm, rather than going in against Conor cold and needing a round to find his groove.