Twine / ChapBook / Change Aspect Ratio HELP!

Been working on a couple of games for a while without thinking aspect ratio would be an issue. I’m now going through and changing design elements to tidy it up before releasing something playable to friends. I’ve searched high and low but can’t seem to find how I change the aspect to suit a computer screen rather than It’s vertical default. Hoping I don’t have to start using a different language and port it all over but I don’t see any info on this.

Any help would be appreciated