Making a reservation on shinkasen

Hi Guys,
Just a quick one. I want to be able to ask how to get a reserved seat ( 指定席) on a shinkansen at a JR Office.
Do I need to specifically state 指定席 in my request or can I just say the following.

すみません、東京から長野まで新幹線で席の予約をどう しますか

Would that be ok?

よろしくお願いします

どうしますか "How about ~" is a question on the point of view of JR or a travel agency. It must be 新幹線の（席の）予約をしたいんですが、どうすればいいでしょうか？ or like that.

Since で can indicates the means (to transfer in this case), 新幹線で席の予約をする is understandable. However, it sounds like you want to reserve something when you are at a Shinkansen seat, because で usually indicates the location of action.

The seats you can reserve are all 指定席. You can't reserve 自由席, so you don't need to say 指定席.

I see Thanks, What I was thinking by the use of で is the mode. i.e 新幹線で by shinkansen. But with your answer "the seats you can reserve"指定席 are on the shinkansen so therefore it is redundant anyway.
Can I use どうすればいいでしょうか as generic "how can I do this? Kind of question? for example if I wanted to go to sapporo could I say。。。
札幌にいきたいんですがどうすればいいでしょうか or would I have to use the conditional form of いく

札幌にいきたいんですがどういきばいいでしょうか

The -ba conditional of 行く is 行けば.

Both are possible, but どうすればいいでしょうか is a general question of "how to do", so it can be used in a situation something like "How can I get a holiday?" or "What should I say to my boss?".

If you say it at a JR Office, it's OK just to say すみません、札幌に行きたいんですが.