In minecraft bedrock edition there are commands like /fill [pos1] [pos2] [Block you Want to Fill it With] [Optional: Mode] [Mode Arguments]
However, getting coordinates, writing them down on paper, ect takes a while, and I feel like for someone who knows how to do command blocks, it would be really easy to just make a tool that sets the positions and runs thhe command for you.
use tool to set 2 corner positions
then put in chat
/fill stone replace air
and you wouldn't have to put the position, you would just be able to do that and then all air will be replaced with stone.