Assuming the value you are looking for is in column A and you want the lookup
results in column C, and you want the value in C to be from the 4th column
from sheet "BBB", then put this formula in cell C1 and copy it down to cell
C835.

=VLOOKUP(A1,BBB!$AI$7:$AL$167,4,FALSE)

The value in column A will be used to search column AI on sheet BBB then
return the value from column AL on sheet BBB to your firs sheet in column C.

Tom