Sure, i assume you are using their reef advantage magnesium product. Plugging this into the calculator:
Means you need to add 3618.6 grams of their product to your tank to get from 1107ppm to 1400ppm. This would be best done following their advice of no more than 25 grams per 20 gallons, you *could add up to 325 grams per day, i would not add that much and take it a little slower.
Your 450ml container holds roughly 2 cups. They recommend 1 cup for each 25 grams, so mix 50 grams of powder in that container, and you can dose it full tilt 4-5 times per day, measuring your mag every other day until you hit 1400ppm. At that pace, (200grams per day) should take about 18 days.
Also from their page:
DO NOT OVERDOSE
Do not exceed 25 g/80 L (20 US gallons) per day. Excess magnesium may enhance the loss of carbonate alkalinity. Do not directly mix with any carbonate supplement. Best if magnesium & carbonate additives are added on alternate days or at least 30 minutes apart.