Dax Funktion for the Previous last 7 days ( Aim = day over day about the last 7 Days from Today)

[Boni]

Hi Community, 
it would be Awsome if some one could Help me! 
I try to Calculate the Previos last 7 days to caculate at the end an Day over day Calculation. At the end I wanted to see how high the Sales have increased oder decreased in the last seven day from today on.
Thanks for Help Guys
Boni 

[Mohammad_Refaei]

It is difficult to answe while you are not sharing anything about the model or the fields.

In general, you need to filter the data field so you will probably use a formula like this:

Last 7 Days Sales =
CALCULATE (
    SUM ( [Sales] ),
    FILTER ( ALL ( [Date Field] ), [Date Field] >= [Date Field] - 7 )
)