Select a chord grid, then click OK.
After inserting chord grids in your score, you can edit their size and position accordingly.
Control-click a chord grid symbol, then choose one of the following from the shortcut menu:
Scale: reduced
Scale: normal
Scale: enlarged
The scaling values are based on the Grid scaling and Chord scaling settings in the File > Project Settings > Score > Chords & Grids pane.
Logic Pro Instruments: PDF