Best way to dub the voice in a very low budget or no budget film
It sounds like you are using your laptop's microphone, and that your main problem is the lack of a quality mic. If you own an iPhone, especially iPhone 5 or later, I would recommend you use the voice recorder app, and email the audio files to yourself using the Share button. The iPhone's microphone is surprisingly good for audio. High end Android phones also tend to have good mics. Using your phone means you don't have to purchase any additional equipment.

If it helps, this guy measured the frequency response of the iPhone 3GS back in 2009, and it's a pretty safe bet that the newer models use mics of either the same or better quality.



Fun fact, the iPhone 5 actually has three microphones. The voice recorder app only takes input from the mic along the bottom edge.



Also make sure you're recording in a very still, closed-off room. If you are editing in Adobe Premiere Pro, syncing the audio to the video afterwards shouldn't be a huge problem!