Alert on last 3 same days count avg

Hi Team ,

I am quite new in Grafana . and facing issue in configuring an alert.

I have daily count of some feed in influxdb .
i want to create alert in grafana on week day basis .
like for Monday it should compare with last 3 Monday Avg.
For Sunday it should compare with last 3 Sunday Avg.
it require because counts differs on weekday and holiday.
I want some thing in alert part
Day 1, it should compare Avg(Day-7 , Day-14 , Day-28) and alert if difference is +_ 7% .