Tools tab > Layout group > 
Viewports menu > Zoom, VPZOOM
Set the scale of a layout viewport relative to the print mode. When you are using layouts, define the drawing scale in the layout viewports and print the drawing in 1:1 scale.
First, move to the layout's design mode. For more instructions, see Workmodes.
Do the following:
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Select the viewport whose scale you want to set.
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Select
Viewports menu > Zoom [scale].If you want to select a different scale, select Zoom 1:? and enter the second number of the scale on the command line.
The program zooms the contents of the viewport to the selected scale.