There are a lot of ways to learn gcode.
I would suggest that a person wanting to learn how to write gcode purchase the book
"CNC Programming Handbook" by Peter Smid. It will give you a firm foundation in basics
and it provides an understanding of gcode. Skip all the other bull,,,, and learn properly
right from the start.
Now on to your question......
Use a different work offset to locate the second circle. IE; G54 for the first circle and G55 for the second. It's just one way of doing it.
RICH