You'll need to process each sheet individually and then stack them:
=LET(data1,'Appollo For Natural Oils'!$A$3:$D$422,data2,'City Tour'!A3:D246,filterdata1,FILTER(data1,(INDEX(data1,0,1)>=G1)*(INDEX(data1,0,1)<=H1)),udata1,UNIQUE(CHOOSECOLS(filterdata1,1,4)),filterdata2,FILTER(data2,(INDEX(data2,0,1)>=G1)*(INDEX(data2,0,1)<=H1)),udata2,UNIQUE(CHOOSECOLS(filterdata2,1,4)),VSTACK(udata1,udata2))