Not surprising that the Royal Park Canvas Ginza does not have concierge, the Royal Park hotels are kind of hotels which does not have concierge. I think the situation with the OP is that OP insist on Michelin Star rating and OP must have a reservation for a restaurant right now. Around Ginza where OP will be staying there are a lot of nice non-Michelin rated sushi places, and I personally think does not has to be Michelin rated. If I were OP I will simply ask for a recommendation from a front desk at the hotel for dinner that day, don't bother making a reservation right now. But OP insist on Michelin Star rating so will require reservation in advance.