You can, by just saying the part a bit loud, so he will notice, in sha Allah.
Your salah will be valid if you correct him in sha Allah.

When praying behind someone who makes mistakes in surat al Fatiha? Should I correct his recitation during the salah? and if I never is my salah invalid?

Prayer | October 10, 2014 4:52 am
Previous

These are the mistakes I found in my salah(s): 1)in one salah, I read ghair-ilmaghD(d for deen)ubi alaihim, is my salah valid? 2)in another salah walaD(a little T’a sound but majority Da came)aalleeen, is my salah valid?
Next

Can a 6year old boy allowed to lead the elders in salah if the boy knows the Quran better than them?