routing a 4 layer PCB
Use a via.

Presumably the power planes are internal. Use a via to connect from the signal planes (top and bottom) to the internal power or ground plane. The via can be completely through the board but only connected to the starting trace and the plane you want.

Depending on your software you'll probably just need to be routing a signal of the same name as the power plane and once you make the via, it will connect automatically.