1.  Okay, I looked at two options, doing it as one amount, or doing it against the donation form that organization. 

2.  No guidance form the IRS on this,

3.  and if I did not just happen to come across an article from a law firm, I would not have know about having to make this adjustment.

1.  I interpret you were referring to the approach of either (1) report the net amount for that donation, or (b) report the gross and add a line with a negative amount to offset.  I think either way would work.  If the amount was significant, or if the client cares (or reads his/her copy with a magnifying glass) , I would consider (b).

2.  If there is guidance from the IRS on everything, @IRonMaN would not have any time for putting jokes in this forum for me.

3.  It is sort of a basic concept that deductions should be net of (i) thingies received in return (from cash donations that come with a meal or a Mel Torme CD, to complex computations for a CRUT....); or (ii) tax or other credits (e.g. research and development expenses used for R&D tax credit; depreciation basis for your pre-2021 Tesla..., computation of qualified education expenses used for the Education credit...) to name a few.  But then, you can always keep reading articles from law firms...