Answer:
If your question is about Robert Zemeckis´s film stared by Tom Hanks, the group that performed while he is playing ping pong is The Doors.
Step-by-step explanation:
There are three songs played while he is learning and finally playing in front of the people in the hospital. The first one is called "Hello, I love you". The second one is "People are strange". And the final song that is when he is playing by himself is called "Break On Through".
These three songs are all from a rock band called the Doors.
I hope this answer helps you.