You need a common factor between both sheets as reference then you can use a Vlookup
I'm on my iPad in class so if it doesn't come out right just pm me and I can send you an example later.
=vlookup(item that you want to match, [item matching1 +however many rows till your date column, # you date column is in relative to item matching, false
Ex
Sheet1 Sheet 2
A B C D E F G H I J A B C D E F G H I J
1 2 3 4 6 1 D 2 4 3 5 6
Code = vlookup(A1,sheet2$A$1$A2, 2, false)
Value in A1 is what it's looking for and matching from sheet 1. Sheet2 is a made up name but it will look like that based onYour other data. but basically just select from the matching cell I happened to make it A1 on the second sheet as well drag from the header until you hit the column your looking for which happens to be column b row 1 on my example. The( 2, false ) will need to be adjusted based on the placement of the column your dates are in in my example they are on column 2 relative to the match in a1. Leave false alone. If you type this code into your specified column It should pull the dates. Make sure and adjust number type to dates or you'll get 4000 numbers