Hi,
You might want to try the mixed Vlookup and IF functions:
=if(iserror(vlookup(b1,$A$1:$A$10,1,false)),b1,vlookup(b1,$A$1:$A$10,1,false))
The above formula is entered into c1, and copy it all the way down until there's no values in column b.
Meaning of the above formula is, if looking up value in B1, exists in column A or range A1 to A10, then retrun the value from Column A, otherwise return the value from B1.
Once the formula is copied down, the reference cell b1 should change, ie formula in c2 would reference to b2, so on.
HTH