I've come across literally hundreds of Irn Bru stains and ALWAYS point them out to the client ( who usually knows ) saying it won't come out, but might fade a bit.
No point in farting about and hoping for miracles.
Although there have been occasions when I've been successful when using HIGH HEAT ( ordinary steam iron through white towel ) along with whichever product you favour for removal of red dyes.
Using the above method YOU WILL GET COLOUR LOSS so be careful, you might need repeated treatments and must be careful of TOO MUCH HEAT.
Is it worth it ?