I’ll have a button for it next update. For the time being, if you’re playing on PC, you can click ‘A’ on your keyboard to pull up the accessibility menu screen with text scaling.
No problem! If you’re interested in knowing other handy shortcuts for Ren’py [this site] has them all listed, but bear in mind that they might not work for all Ren’py-made games because they seem to be dependent on the versions.