A 90 ATAR might be a bit of a challenge in your current case, but that doesn’t mean it’s not achievable. It also depends on how much time you spend studying/you’re willing to spend studying. If you can reach 85 across all your subjects, your goal will become easier to achieve. Tutoring might help you improve academically so you could give it a try. However, remember that going tutoring alone isn’t sufficient. You have to put in effort and be diligent so you can get better marks.
You could allocate more of your study time towards Physics in addition to tutoring and assistance from your teacher and see whether this strategy can help you improve in Physics. Alternatively, you should consider whether Physics is for you and whether it is a subject you may want to drop.
I hope this helps!