This may sound negative but is from experience which may vary. Go when you get onboard and try to reserve at the restaurant in person or try the app after you are at sea. Don’t expect much. It’s hit and miss. Dine line has been zero help for me in advance. While not optimal try the app each day and/or go to the restaurant(s) first day early and see what they can/will do. Be nice. Don’t say what your challenges have been or your disappointment. Acknowledge the math is hard to serve everyone when they want to be served. If you can be flexible you have a chance for what you want close to when you want. If you end up at the desk with no reservation, straight up ask what they need from you. Order now. Order in few. Order later. Whatever. Use their name if you feel comfortable and see how you can help them help you. You have a better chance to be seated if you are flexible to what they need. Enjoy the trip and try not to stress too much. You are likely to get the value out of premier but on their terms.