There are two ways of creating additional month grids. One is using a ready-made template - you'll find one of these under Yearly (12-page) calendars.
If you would like the additional month grids with a different design, use the second way.
Here are the steps:
Create the base layout with a single month grid (e.g. January). Right-click on the main month grid and select Copy, then right-click on the canvas and select Paste.
Double-click on the copied grid - this will open the grid editor. Switch from Cells to Month and select the necessary month here (e.g. February). You can select a different design for the additional grid by clicking Select Style.
Create the other copy (for the previous month) in the same way. Resize and position both copies as you wish for creating your own calendar design.