How to correctly implement data output by dates through FireBase [Kotlin]??

Question

Android

There is an application that collects data, namely rait : from 1 to 5, date I need to display

the average number for certain periods: 7 days, a month, 3 months, 6 months, 9 months, 1 year
7 days etc. (it’s just that there may not be data for a year, but a conclusion is necessary) (I know how to implement the formula for implementing the average indicator for a period, but I don’t know how for a certain time)
Tell me I broke my head