I tried ctrl- which was suggested somewhere online, but that makes the font smaller. (ctrl+ though does not undo that, so I had to restart LightTable to get back to normal).
Pressing ctrl enter I can manage to write and use "jump to definition", but obviously I will not be going through that every time....
If this should have helped, it is rather confusing what the period and comma here mean:

So do the built-in default keyboard shortcuts allow that, and how do they allow increasing font size?
cmd/ctrl+enterin the pane that this brought in: type "jump to" to see the command "jump to...", plus its keyboard shortcut. you can select the command from there but that would suck if it were the only way to invoke commands, so observer the keyboard binding you get there: (in the blue circles below)
Courtesy of @rundis from the gitter channel...