We can select all worksheets in a workbook firstly, and then change these worksheets’ orientations together. You can do as follows:

Step 1: Right click one sheet in the Sheet Tabs bar, and then select the Select All Sheets from the right-clicking menu.

Now all sheets in current workbook are selected together.
Note: For selecting all sheets with shortcuts, you can also select the first sheet in the Sheet Tabs bar, pressing the Shift key and then select the last sheet.

Step 2: Click the Page Layout > Orientation > Landscape.

Step 3: Keep selecting all sheets in the Sheet Tabs bar, right click one sheet and select Ungroup Sheets from the right-clicking menu.

Now all sheets have been changed to the landscape orientation already.

Apart from selecting all sheets and then batch changing all sheets’ orientation, Kutools for Excel’s Copy Page Setup utility also can make all sheets to landscape orientation easily.

Step 1: Make active worksheet to landscape orientation with clicking the Page Layout > Orientation > Landscape.

Step 2: Click the Kutools Plus > Printing > Copy Page Setup.

Step 3: In the opening Copy Page Setup dialog box, keep selecting all sheets in the Sheet box, and only check the Orientation on the Page tab in the Page Setup box, and then click the Ok button.

Now all sheets in current workbook have been changed to landscape orientation already.

Copy Excel page setup to other worksheets in Excel