Hi Deepika,
When you select the button for Delta you will get the records that will get pulled in your next Delta run.When you select the button for Repeat Delta it will give you the records which will get pulled in case your previous delta had failed and you had marked the request red in your PSA as well as target.Thus Repeat Delta button will give you the new delta records in addition to the failed delta records.
Regards,
Shalaka