If HAL isn’t driving. 
I’d presume that it could be done with celestial tables, a sextant and lots of extra gas, air and food. From star sighting you could tell where you are. You’d need to know where Earth is, and where it will be when you get home. There would be lots of course changes, hence the extra food, fuel and air.
NASA really fell down explaining this stuff to the public. Unmanned missions had found a lot of titanium in lunar soils. Titanium is a known human immunosuppressant. The quarantine was to protect the astronauts from getting sick. After a couple of missions it was seen to be less of a problem than feared, so NASA could cut out the quarantines. Moon germs were easy to explain, but a zillion-to-one shot.
How exactly were the astronauts exposed to lunar soil?
When they took off their helmets after walking on the moon. Their spacesuits were covered with moon dust. The LEM barely had room fir the astronauts, let alone a shower. I don’t know how well the soil sampled were sealed.
Lunar dust is surprisingly sticky. It’s not rounded at all on a microscopic scale, but instead made up of sharp-edged jagged fragments. When the astronauts walked on the moon, they got dust all over their boots and legs. The lunar lander didn’t have an airlock - they had to decompress the entire cabin to leave - so when they came back in and re-pressurized it, dust from their suits got everywhere.
This is a major concern for future lunar missions. In addition to being possibly mildly toxic, lunar dust is terrifically abrasive, and tends to wreck seals and bearings aver repeated cycles. And it also gets everywhere. This is why some of the more recent plans NASA has come up with involve suits that have a big hatch on the backpack that docks to the lander/rover, so the suit itself never has to come inside.
I wasn’t aware of that, thank you!
Minor nitpick - Irwin didn’t suffer his cardiac event while on the lunar surface. It was observed by NASA while the crew was in lunar orbit preparing to return to the Earth. In fact, doctors noted he was in the best place for it to occur, because he was in zero gravity, so nearly weightless.