Tracking by the nutrition label is basically doing calorie counting. You are accounting for the calories of the alcohol macro-nutrient which is 7 calories per gram and myfitnesspal will have the carb info of the beer from the nutrition label. There is nothing wrong with doing it this way and it will still make you aware of the calories that you are consuming.
When people are utilizing IIFYM, they are solely looking at protein, carbs and fat and counting those in grams.
Therefore to answer your question, you would create your own entry being 24g of carbs. The idea behind it is that you would consume at least 24 grams of carbs in your meals. This way you are still in a deficit calorie-wise even with the beer.
My daily goals are 135g of protein, 180g of carbs and 60g of fat. Each day I do my best to hit my protein goal then I interchange carbs and fat depending on what I'm eating...I'm not as strict on those. If I happen to eat more carbs one day and I want to have a glass of red wine that night, then I exchange the alcohol calories in the glass for the fat calories, if that's where I have room. Therefore, using the example below, I would eat about 14 less grams of fat.
RED WINE 5 OZ.
- 5oz. red wine = 129 calories
- 129 / 4 = 32g carb
- 129 / 9 = 14g fat
- You could decide to record it and as 16g carb and 7g fat
Another suggestion for macro counting is to change your tracking window. For example, I wasn't very good at pre-planning by entering everything a day before and following that strictly. So instead I changed my 24 hour tracking window from about 6pm-6pm, meaning I will input what I eat for dinner tonight on tomorrow's dinner entry, then I just plan tomorrow's breakfast, lunch, snack, etc around what I have eaten for dinner. It helps me with having a little more flexibility in case I go out to dinner, for example.