Hourly Count for last 30 Days

Hello,

Im using below query to get Count results for today.

Declare @Hours Table (Hour int);
Declare @i as int;
Set @i = 0
While @i < 23
Begin
   Insert into @Hours
   Values(@i);
   Set @i = @i + 1;
End;

Select
   [Hour of Day],
   Count(SERL_NBR) AS [Serial]
From
(
   SELECT DATEPART(HOUR, PART_TST_TS) AS [Hour of Day] , SERL_NBR
   FROM JCIMWhitby.dbo.REPL_TRH REPL_TRH
   WHERE (REPL_TRH.PART_LOT_DSC Like 'FRT Audit%') AND DATEDIFF(day, PART_TST_TS, GETDATE()) = 0
   Union ALL
  
   SELECT Hour, NULL
   From @Hours

) as [DATA]
GROUP BY [Hour of Day]
ORDER BY [Hour of Day]

How do I query count like this for last 30 days. Any help is appreciated. TX