I wanna get rid of some water inside this build, but I don't know if I can specifically delete just the water. And sponges don't seem to be doing squat.
Don't know about blingedit, but worldedit will do that easily.
To tell them how to live is to prevent them living.
Sadly there's no worldedit for 1.13.2 that I know of.
Sponges or wait for Worldedit to update. Or the old school method of dropping sand or gravel into it and dig it out. If you want to install mods, there are a couple that will do it, like RF Tools.