Hello, Alexis,

I can see two options:

1) The fastest way is to add an Expression, for example:
=IF(fieldName= 'C', 'Credit', 'Pay Off' )

2) Or you can add it to your source query for this report

I am confused
is any example of this

It's just 2-step operation:
a. Drag Expression control to report
b. Input =IF(fieldName= 'C', 'Credit', 'Pay Off' ) in the dialog which shows up after dragging.

The documentation (with examples and video) for an Expression field:

ok
thanks is working