By default, each grid color of the Blog module, while the Grid layout is being used, is set to be
5.5% which is also the default value of the Row's Gutter.
Change the space between each Blog module's grid column using Row's Gutter width
Open the Row's settings that contain the Blog module.
Go to Desing Tab → Spacing.
Enable Use Custom Gutter width.
widthvalue - the default value is