I think you basically just need experience/practice. Imagine lifeguarding: they don’t just explain it to you and then hope you remember what to do the first time you see someone you think might be drowning. They train you and have you ‘rescue’ people in a controlled environment, so that when the real thing happens, you’re performing something you’ve done many times.

To put it another way, you don’t want to think faster. You want to have already thought about it, and already prepared for what to do.

Depending on the extent of what you want to do, maybe a few friends and you can try to rehearse your response. Have them simulate (without telling you exactly when) some of the signs of a seizure, then try to identify it and give their phone a call as if you were calling emergency services.

If you want to go further you can look into various first aid certs. Most classes are like $20-60, and they’ll be able to prepare you far better than anything else.

For context: Not the same thing exactly but I had to get first aid certifications in the context of bringing small groups of people into semi-remote areas of nature. Type of thing where you probably have cell service but it may take hours for help to arrive. We did a lot of practice on each other.