How can I study while I feel tired?

When you feel tired? You can, but you'll fail at it.
What I would suggest is when you're tired and cannot focus just do something else that makes you relax.
Snooze, meditate, play an instrument etc. Take your pick rly.
Don't push too hard, because in the end you'll break. Take it easy!

Do ten burpees. As Jocko Willinck says, it’s impossible to feel tired after doing ten burpees. This has a knock-on effect because studying immediately after exercise makes learning 74% more effective (can’t remember the study but I used it for a university essay recently, so it’s academic)