Hit F12 and your browser will pop up a Javascript console window to the right of the VN. I'm going to paste this screenshot of my chromium with the javascript console open. Note that I've already done the things that I will talk about next.
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The first thing I did was type "Sugarcube.State.variables.charge" at the ">" prompt in that window and hit enter. That returns a 0 which is the current charge on the phone as you can see in the content window as "Charge: 0". Note that as you type, the console will automatically populate a popdown list with possible completions. So after typing only "Sugar" I can just hit the right arrow key and it will fill that out as "SugarCube". Then I typed ".State.var" and that was enough to let me hit the right arrow key again to have it fill out "variables". So you don't have to type all this everytime and worry about it being incorrect.
I hit the "up arrow" key to recall all of that and just typed "=40" to set it to 40. Note that the content window on the left is in suspended animation while the console is open. So that "Charge: 0" won't change to "Charge: 40" until after I close the console window by clicking the "x" gadget in its upper right and then click something to go into the next passage.
I did "up arrow" again and then used backspace to erase the ".charge". This showed all of the variables in effect for the VN but as a "closed two line tree between "{" and "}" with a small ellipses "..." at the very right. To open it up as the full scrollable list I clicked on that "..." and we see the first page full of variables and values. I can now use "up arrow" and then type out individual variable names to peek and then use "=" with a new value to poke.
Congratulations. You now know how to hack 95% of Twine games since just about everybody uses SugarCube format and don't know how to change where the variable storage is hidden.