"+>" - adds a blank cell in the currently selected position shifting the following part of the chord progression of one beat/cell forward.
For example tap in the first space top left and tap the Plus button 16 times to create space across the top to add space for an intro.
Here is an example to spread out the chords.
 
You can make bars half as wide if you delete the spaces in the bar.
"<x" - removes the current cell, moving the rest of the chord progression backwards one beat/cell.
To delete a whole measure you’ll need to tap the Delete Beat four times (if that’s how many cells were used for the measure).