Good answers by rockrose. And I would add that there are a lot of things that can screw up an IQ test such as thyroid problems, ADHD, ADD, etc and give a completely false reading. The age of the child is also important. So it would be helpful to have a bit more information.
You don't give a lot of details, but as always, lots of exposure to different stimulus is important - very interesting vacations, interesting conversations, hands on stuff like creating kites or go carts, reading for pleasure, etc., are all a part of optimizing IQ.
You don't say what age your child is or how low the IQ is suspected, but starting early with career options that would be appropriate to his IQ level would be helpful too.
And I think it's great that you aren't accepting he has a low IQ - expect a lot, and you'll probably be rewarded.
Best wishes.