Back from the Dead

Trimming fat is directly about calorie intake. Nutrition can affect fat loss indirectly through fatigue or appetite, but the direct link is still calories.

If you want to keep the muscle, get overall good nutrition, especially (but not exclusively) ample protein. The MFP defaults usually aren't a terrible starting point for most people, as long as they don't cut calories silly far to aim at fast fat loss. You'd want to lose fat at a moderate pace anyway, for best odds of keeping those muscles you've worked so diligently to build.

Beyond that, to maybe fine tune, this is an evidence-based protein estimator and guide:

https://examine.com/protein-intake-calculator/
https://examine.com/guides/protein-intake/

If you're substantially overweight, it's OK to use goal weight in the calculator (it says that somewhere in the guide).

Fats, for a male, maybe 0.3-0.45g daily per pound of bodyweight (women would be better off 0.35-0.45 IMO).

Try to get a well-rounded complement of micronutrients, fiber, beneficial phytochemicals, and probiotics . . . mostly from food, if possible, but supplements are OK in most cases if you come up short. Common food sources of those are veggies and fruits.

When it comes to calorie goal, get a starting estimate from MFP (or some other calculator, but realize that most outside calculators use different assumptions). Follow that pretty closely for 4-6 weeks, then look at your average weight loss per week. If that's not in line with your loss goals, adjust calorie intake. (The calculators spit out statistical averages. You're an individual, and individuals may vary from average, either high or low.)

The multi-week trial is because water and digestive weight fluctuations can be surprisingly large, mask fat loss on the bodyweight scale, and make it hard to assess fat loss rate. Going with a few weeks will average out some of that variability.

You don't have to be exactly exact on nutrients every day, nor do you need to fix every single thing all at once. Log your food, see where you may be coming up short, and tweak your routine eating habits (ideally using foods you enjoy) to dial in improvements. If you're not diagnosed with a deficiency or relevant serious health condition, you can take some time working on nutrition, both the learning and the doing. Even in the long run, close to goals on average over a small number of days is fine.

Best wishes!