Hi.

I have data in sheet 1 like below

Custid loc city
123 us newyork
124 uk wales
876 in mumbai
Sheet 2
custid newcustomerid
123 756
124 394

Outputsheet:
Custid loc city
756 us newyork
394 uk wales
876 in mumbai

So it will check sheet1 custid with sheet2 custid
If both matches it will replace custid with newcustid.if cust id not exists it will load sheet1 recprds as usual