He lost 15 units of blood and ended up in hospital for 23 days.
While there were others already at the scene, McDowell was the first of the two lifeguards to arrive.
"[Gallagher] was the main priority because I really thought he was going to die," McDowell said.
"He was in and out of consciousness. I was saying words of affirmation, telling him he was going to be okay to keep him with us because if he fainted or passed out we weren't going to get him back."
Gallagher said he remembered "hyperventilation and drifting off".
"I remember Andy yelling at me 'Deeply' — to breath deeply — and I did and it worked."
Te Hiini looked to McDowell for advice and was sent to settle the driver of the car, who had also been injured.
Te Hiini said he had a good idea of what to do because part of his surf lifesaving training had involved car crash scenarios.
"I'm stoked I could help," he said.
As McDowell drove towards the scene, people driving in the opposite direction were flashing their lights at him.
"I just assumed it had happened a while ago, but when I got there, the bike was still on top of him."
He said those people should have stopped to help, but he thinks people would not stop as they did not know how to respond — which is why he was pleased Gallagher's donation would go towards improving first aid skills.
"The idea is to get more people through first aid so there are more people running around with first aid tickets," Gallagher said.
Gallagher worked as a locomotive engineer with Kiwirail prior to the crash, and is unsure if he would be able to return to the same job.
"But Kiwirail have been massively supportive — they will retain me and retrain me."
McDowell said it was good to be able to use the skills learned as a lifeguard in a different emergency situation to the beach.
Gallagher said it had been a hard road so far and with an accident like his, he has had to rely on support.
He said he wanted to thank friends and family, and especially his wife Nikki, who have needed to help him on a daily basis.
"This is what keeps me positive."