Split/filter infinite Calendar by weeks

Please try at
C39
=IFERROR(INDEX($C6:$AG6,MATCH(C$38,$C$5:$AG$5,))&"","")

or
=IFERROR(INDEX($C$6:$AG$27,MATCH($A39,$A$6:$A$27,),MATCH(C$38,$C$5:$AG$5,))&"","")