This is a truly difficult situation. I know, because I've been in it and don't know that I always fared too well. I've stayed silent, so that I didn't draw the wrath of others who were putting down Christians, I'm very ashamed to say. It's especially difficult when someone is standing there, putting down Christians saying, give me the proof.
The Bible says in Romans 1: 16 For I am
not ashamed of the gospel of Christ: for it is the power of God unto salvation
to every one that believeth: to the Jew first, and also to the Greek. 17 For therein is the righteousness of God revealed
from faith to faith: as it is written, The just shall live by faith.
Although I can't take away all the times that I didn't stand up for my faith the way Jesus would have wanted, He still forgave me when I asked Him and in that, I am so very, very blessed!
I've prayed for ways to help people come to know and love Jesus and all He's given for our salvation. Although I'm not always quick with giving proof to those who challenge the Christian faith, Jesus has led me to create blogs that show this proof.
For those who don't believe that Jesus is God's Son, they can go to this link: How to Know Jesus is God's Son at https://jesusissonofgod.blogspot.com/
For those who doubt God created the world, they can go to this link: Creation: What's It Matter? at https://creation-matters.blogspot.com/
For those who have more questions about God, they can go to this link: Video Answers About God, Jesus, Creation, Disaster, Etc.via You Tube found at https://videoanswersaboutgod.blogspot.com/