Short answer: yes, you should force him. Any ear infection is uncomfortable, itches or even hurts. If you don't treat the infection, there's a risk that it becomes chronic and the discomfort never goes away again. One of our cats went missing for a year and came back with a very severe ear infection. He scratched his cheeks bloody for months and even went deaf on one ear. (Since the ear canal bends towards the nose inside the skull, cats tend to scratch their cheeks instead of their ears when they have an inner ear infection)
Before you even start treating him, prepare everything you need. The shorter the treatment lasts, the less stress for your cat. Having to stand up and grab the medicine prolongs the stress. Have everything you need at arms reach, have every medicine bottle opened and ready to be used, and have a tasty treat nearby to reward your cat.
The best way to treat your cat is to stay calm. Animals react to slightest signs of anxiety and get anxious hemselves. Pet your cat, do the "lazy cat blink" at him to calm him down before treatment.
Then grab and pinch the skin on his neck. This instinctively paralyses him for the duration you pinch his neck and reduces the risk of you causing him pain when he thrashes around.
Quickly apply the medicine to the entrance of the ear. Do not stick the medicine bottle deeply into the ear! That can cause even more damage and isn't nesseccary at all. You can spread the medicine by massaging the ear in circular motions.
Before you release the neck of your cat, hold the treat (like a piece of hotdog wiener) in front of his nose to let him smell it. Then let him go. Either he is so distracted by the treat that he forgets the treatment for a moment or he runs away. Give him the treat anyways to connect the treatment with at least some positive experiences.