The page describes a daily serving of one to two gummies. That is a range, and it leaves the choice to you.
The difference between one and two gummies is a doubling of every ingredient, and the amounts are not published. It also changes how long a bottle lasts and what you spend per day.
The page does not say what should lead you to one gummy rather than two, or whether there is a reason to start at one.
The Supplement Facts panel on the bottle is the authority: it states the serving size and what is in it. If the label and the page disagree, follow the label and ask the seller in writing. If you take medication or have a health condition, ask your doctor which end of the range, if either, is sensible for you. Do not go above the labeled serving.