As other people are saying, being tested for and treating sleep apnea is a good first step - IF IT IS SLEEP APNEA. What many people don't realize it's that loud snoring is not exclusive to apnea. It is an indicator of it, but one can indeed be a loud snorer and not have apnea. Additionally, there are multiple kinds of apnea that cannot all be treated in the same way. There's the CPAP machine, the nose guard, wedge cushions to lay in your side, surgery, implantable device, weight loss of overweight, and so many more. When the snoring is not due to a one if the apneas or another easily identifiable cause, the are tongue and throat exercises that have become popular recently to a certain degree of anecdotal success. Drinking a certain beverage right before bed. Medications/supplements. Weird stuff
Because there are hundreds of potential causes (and even more potential solutions, more than half of which only kind of work with some people) and the only thing we know is that he snores - there's no answer that can be given except to say a doctor needs to pinpoint the cause. My guess is your dad is an adult and know he snores, and still doesn't feel the need to go to a doctor, you are asking because it bothers you? If it's not leading to an effect in his health, then there's not much to worry about (eg, he not waking up still exhausted, or waking himself in the middle of the night by gasping for breath, waking up with a sore throat or headache, etc) and going through those tests is going to be crazy expensive even with insurance (assuming you are in the US)
With the family I grew up in, it be hard to convince you the house wasn't a sawmill with how many logs all of us were sawing every night. My sister was the only one between my parents and my siblings and I that didn't snore. She used to complain about it, but now she sees it as reassuring because she can keep track of where we all are in the house and that we're all still alive (this is mostly for our parents who are now much older - them snoring at least means they aren't dead), if we're still awake or if she can sneak Christmas presents down to the tree, in the morning she can tell whose woken up and whose still asleep. And yes - every single one of us has spent multiple thousands of dollars (after insurance) to found out there's literally nothing we can do, there's no position we can sleep in to change the fact that we snore, there's no tongue exercises that will fix it, no magic pill. That's not to say that will be the case with your dad, but trying to give you realistic expectations.
Given the financial situation (and the fact that it takes months to get a sleep study approved), you can try ear plugs or a sound machine. When I was in my younger years and would share hotel rooms with friends, I would preemptively bring these for them, which they say helped