The best way may be to use an illustration that you think of either from their life or from your own life.
The Hebrew word for repentance means returning. The prodigal son is a story like that: he goes away from home, and he returns home (Luke 15:11-32).
I’ve sometimes used this illustration: one night when we were in Glasgow I was driving down the freeway on my way to church, and going up the other direction I noticed the car of one of my elders. I knew it was his car because it was the only elder who had a personalized number plate. I thought, “Why is he not going to church?” Then I realized I was actually heading in the opposite direction. No matter how fast I traveled or how far I went in that direction, I would never arrive at my proper destination. So I had to turn around to get there.
That’s the word picture of repentance. It’s turning around. It’s understanding you’ve been facing away from the Lord and you need to turn around in order to come and trust Him.
Repentance and faith are really two sides of the same coin.