I finally figured this out. This is really bad user experience in the desktop application. Double clicking into a field should allow you to override that field's content. It was not obvious, but here is the solution. I removed the edits I made to that worksheet, as that was not the appropriate way to do it. And I did this because I figured out how to edit the field.
So you click into the field first. You will notice you can't change anything (unlike other fields, hence the confusion). Then go to the menu bar and click on "Edit" then click on "override". You can then enter whatever number you want. But in fact, there are two fields to the left of the total, which are not obvious. Essentially the area you see the "..." text. Click somewhere in there, and you will be in an edit field. The far left box, is where you will enter the text "IRC 1341". To the right of that box (NOT THE TOTAL VALUE BOX), you can enter text (only numbers). This is where you enter the amount of the claim to right credit. Once you enter it into this field, you will then see that the value in line 78 will now include that credit amount in the total.
So to recap, you won't override the total amount in line 78, but you need to click that field to do the Edit -> Override setting so that you can then click into the two fields to the left of that total field.
Then you can exit out of the Form view and you will see your total credit amount has increased by the amount of the Claim of Right credit.
Good luck!
