Connect IT scenario, to copy old value from destination

Hi Team,

I have a requirement, where i need to compare the values from source and destination, based on the result i need to filter  and send sata to destination. 

For example,  I have a field in destination. i need to check that field value is null or not null. If it is null, then i need to consider value from source. If it is not null, then i need to ignore the value to be copying into destination.  

Destination is Excel, source is Service Manager database(ODC Connection)

How to do that?

Suggestions are appreciated.

Thank You. 

Regards,

Shalini R