If you have claims that have been adjudicated by another payer, you can drill down and see the adjustment decisions this other payer made. This information is in the 837 claim as it came in.

Claim lines with prior payments by another payer.
If we double-click into the field we see the details in a pop-up form

Drill down view into COB payment on the claim line level.
If we want to adjudicate the line and click on go, we see that an adjustment for the already paid portion of the service line is already generated in the form.

The line adjudication window shows a payment by another payer automatically as adjustment.