There are two ways to reflect this in the tool. You can indicate cover crops in the assessment of the crop that is preceded by a cover crop. Nothing should be indicated in the assessment of crops for which you don’t grow cover crops.
Alternatively, you can distribute the carbon sink benefits across all crops in the rotation, e.g. if you grow cover crops in 4 out of 5 years on the whole field in rotation, you can indicate 80% cover crops in all crop assessments. The latter is safer as it is a more accurate reflection of reality.