The questions we must first ask in relation to our question:
How is God different from humans?
What is God ‘made’ of?
When was God ‘made’?
The question "Who made God?" is a question that implies that God is not all-powerful if He was made, as whoever made God would have to be more powerful.
The solution to this comes from how we have lost the understanding of what God means in Christian doctrine. God, by definition, is a being who is timeless, spaceless, and immaterial.
If something is timeless, can it have a beginning? If something is spaceless, can it have limits? If something is immaterial, can it be reduced solely to a physical presence?
The answer to all these is no. God is the first cause, and through Him all things came into being, including space, time, and matter.
Conclusion
Understanding that God is not bound to human constraints, such as time or a body, is difficult to conceptualize, but it explains how He can be omnipresent and without a maker or a beginning.