Is it considered academic misconduct as a tutor to help your student with homework that is for marks?
It is unethical to do their work for them. It is certainly ethical to teach them how to do their work. But somewhere in between those is a dividing line so it takes some finesse.
Ideally, as a professor, when a student asks for help on an assignment, I'll try to determine why they have a block that is holding them back and then try to clear that block with some minimal hint that lets them have an insight. Of course, this requires a back and forth conversation to discover what they have tried and why they have taken the approach they have done. It also assumes that they have made some initial effort before you start.
For a tutor, especially one who could be in contact with the professor, it is actually easier than for the professor or a TA, since the scale is 1-1, rather than many-1. A professor may not have time to follow through with each needy student according to the ideal.
But, as long as you stay focused on the learning and unblocking then you should be fine.