Since you have a carb goal in mind, calculation is fairly easy:

Set MFP to whatever calorie goal you want (Goals -> Custom), then set your carbs to whatever percentage yields about 100g. This will probably be the 10% or 15% setting for your calorie range.

Calculate the amount of protein you need --> .8-1g/lb (or 1.9-2.2g/kg if you do metric) of lean body weight (more if you're doing a lot of exercise, less if you don't do much), that way you maintain you keep the muscle you have and your weight loss will favor body fat. To get lean body weight, find out your body fat percentage, then convert that to a weight, then subtract that weight from your total weight. This will be around the 30% option.

Set the rest as fat. Yes, this will be around 50% or 60%, and yes, it will be upwards of 100g+. This is not a bad thing, and it's important you get enough, because going low carb means you need to get your fuel from somewhere else (and protein is an inferior fuel source to carbs and fat, and going high protein, low carb, low fat is a recipe for disaster). You should never go under .45g/lb of total body weight, because you need that fat to properly absorb nutrients. Just get your fats from high quality sources, such as pastured animals fed species appropriate diets (grass for cows, omnivorous diets including foraging for pigs and poultry, etc), fatty fish, avocados, coconut, and olive oils. When obtained from quality sources, the fats that you eat should largely be monounsaturated (believe it or not, animal fats are largely monounsaturated when the animals have been raised properly), some saturated fats (this isn't a bad thing, your body needs saturated fats to work properly), and a small amount of polyunsaturated fats (primarily Omega-3 and Omega-6 fats, in a 1:2 or 1:1 ratio of O3 to O6).

I have my calories set to 2200. My macros are set at 30% carb, 30% protein and 40% fat. Most days I only get to a net of 2000 to 2100.