This is not similar to homework and asking such a question is not evidence that you may not be qualified for this job.
We can't do the work for you, but that is not what you need. What the panel will be looking for is not necessarily specific answers. In fact, if the panel ask you the questions you have listed, (they may not, the questions may be different), what they are looking for is your process. Those questions have a range of different answers, and if they ask 10 equally knowledgeable candidates, they are likely to get 10 different but equally acceptable answers.
The point is, it is your reaction to the questions that will help you, and how you tackle them. For instance, in answer to the first question;
"List the first 5 steps you would take to diagnose a virus", I would firstly say, (politely), that there is no set lists of steps, rather there might come a realization that there is "something amiss". Then I would go on to say I would look for behavior in the computer that is unexpected and unusual. What is that behavior?
I would then talk about 4 steps, (note I have already said the first step), that I would do. What would you do if you noted unexpected or unusual behavior? Would you check the Task Manager to see if there is any unusual process listed? Would you immediately scan with your anti-virus utility? Consider what you would do. List them down before the interview and talk to yourself about them, as if you were guiding someone else, a close friend or relative, etc. Practice on yourself before the interview.
It may be that the question is loaded. For example, if your 2nd step would be to scan, then do you need other steps if the scan finds anything? That might be a relevant answer in itself.
With question 2; "List the first 5 steps you would take to clear a computer of a virus". you may already have taken one of the steps. The two questions may be closely linked.
Then you move onto Customer Help. Very different from the first two questions where you are diagnosing something for yourself. With customer help you are the guide and you have to help the customer through what you might want to do to resolve the issue. Remember that you have to visualize the situation, so a description of it is vital. Is that the first step? Remember also that, although you may take the customer through 5 steps, you may not be able to resolve the issue. The panel are not looking for that. They are looking for what you would do.
An example. The customer asks a question you don't know the answer to straight away. It is OK to say that to a customer and promise to follow it up and phone them back. If you do phone them back then that is good customer service.
As to the last question you say you know what it does. If that's the case, then ask yourself why you, or anyone else, would need to do such a thing. If you were asking the question of someone else, what would you expect them to say?
Note, the questions may be different. There may not be any single answers and some of the answers may not point to a successful solution of any hypothetical situation. Don't be afraid to say to the panel, "I don't know", but if you have to say that, don't just stop there, say "I don't know, but........", but what would you next?
I hope that helps. Interviewing is all about technique and confidence, not necessarily about right answers.