“Something is missing” is a useful observation, but it does not yet tell you what to add. Salt, acid, heat, and richness change a dish in different ways.
Put a spoonful into a small bowl. Try a few drops of lemon in that sample, or a tiny pinch of salt, and taste. If the improvement is clear, make a restrained adjustment to the main pan. Stir and taste again before repeating.
This is especially useful when cooking with unfamiliar stock or canned ingredients. They may already supply more salt than expected. It also helps when somebody suggests a strong seasoning you are unsure about.
Keep tasting hygienic: use a clean spoon each time or transfer the sample without returning a used utensil to shared food. The test is meant to reduce uncertainty, not create a new problem.
A short example at the stove
Imagine a pot of white beans that tastes heavy but already salty. More stock may make it saltier. A separate spoonful with two drops of lemon lets you check whether acidity is the missing contrast. If that helps, add a small amount to the pan and stop before the beans taste overtly lemony.
Now imagine the same beans taste sharp and thin. Lemon would push them farther in the wrong direction. They may need more gentle cooking, a little suitable fat, or a change in the proportion of beans to liquid. The tasting method has not changed, but the answer has.
You can also pause. Very hot food is difficult to judge, and repeated tasting can make differences less obvious. Let a small sample cool enough to taste comfortably. Keep the main dish under appropriate cooking or holding conditions while you decide.