RMD 2020 partially returned

[nytcpa2012]

A client took his 2020 RMD before knowing he didn't have to.  The stocks sold to do this had lost value by the time he repurchased them (down by $8,055) so he thinks he shouldn't have to pay tax on the difference since he sold/then purchased back (not within 30 days) the same # of shares of same stock.

I've explained that the IRS would no longer have the opportunity to tax that $8,055 (since already lost), it is taxable.  Is there something else I can refer him to to support my thinking?  He has received the 5498 showing the contribution.  Should I show the original distribution as all taxable (since it's coded that way on the 1099), or can I use the rollover code for all but the 8055? 

[Just-Lisa-Now-]

Im not following you...he took out $XX and put $XX back into the account, right?

Im not sure what stock prices have to do with anything.