Prometheus alert -> how to create such subquery

Hi I need to prepare prometheus alert, I got query (sum(increase(input_data_validation_total{result="PRESENT"}[15m] offset 1w)) by (field) / sum(increase(input_data_validation_total{}[15m] offset 1w)) by (field)) > 0.9
This query return fields from last week that got percent occurence more than 0.9. I want to get know if some of this field now got smaller occurence compare to last week.
For example first query returns field ‘a’ with score 0.99 so I want get field ‘a’ if now it’s lower for example 0.98. I guess it should be created as subquery but I don’t know how to create it. Thank you for help