Begin with a recipe you can repeat: the same beans, measured coffee and water, the same brewer, and a consistent pouring or stirring routine. Record the grinder setting and the approximate time. Numbers printed on two different grinders are not directly comparable, so treat your setting as a local reference.
Taste the coffee as it cools and describe the problem before changing anything. If a brew seems sharp and thin, try a small step finer; if it seems harsh and drying, try a small step coarser. These are experiments, not diagnoses: uneven flow, water, roast, or an unsuitable ratio can produce overlapping impressions.
Keep the other variables steady for the next cup. Note whether sweetness, clarity, and texture improved, rather than judging only by brew time. If several grind changes fail to help, return to your baseline and examine one other variable. Changing grind, temperature, dose, and pouring together hides which decision made a difference.
The conversation
A good question can make a better brew.