1. I’d make myself known as a member of staff by asking whether the tourist is OK or needs help - he might need reassuring or calming down if he is stressed or panicky. I must listen carefully to what he wants/where he wants to go and then try to find the quickest and easiest route from the station to Heathrow. If he has to change lines along the way, I have to check whether there are lifts to help him change lines as easily as possible. Because the tourist is elderly, I would consider helping him to the platform with his luggage. I will reassure the him again and try and let him know exactly what will happen once I get him to the platform. Before ensuring he gets onto the right train, I’d considering calling up other staff at Heathrow to ask whether I could get another member of staff at that station to meet the tourist there, though I’d ask whether this is okay with him first.
2. I think that the most important thing is to reassure the man, then help identify the route that needs to be taken, so that the customer actually gets to the destination and is relaxed. As to why I would do this, the man is probably new to the country, worried or confused, and my approach to the situation may help prevent him from getting lost in future, and let him know he can trust the staff to help him with anything.
This is something along the lines of what I put on my application. I'm assuming this was your 'hypothetical situation' question, so don't bother waffling on about what Underground lines you need and all that - the question is simply a test of what practical steps you would take in the situation, not a theory test. Your options are endless.