You need more information:
Final Size after cutting pages (probably A4?)?
If the final size is different, you have to correct it too.
To change size and bleed go to File > Document Setup…
You will also have problems with different text flow if you need to change the final size.
But I need to scale it down not to resize the design. Meaning, scale it down & sending it for printing as PDF file. So text flow and all design elements will not be affected with the resized design.
Select the Page tool. Select all your pages in the Pages panel. In the Control Bar, for Liquid Page Rule, select Scale. Input your new width and height.
To be honest, I haven't much experience with Liquid Layouts, as I have a (possibly rational) aversion to changing page sizes after doing the layout work, so someone might be able to suggest a better way. With shorter documents like posters, when the size changes at the last minute, I usually place the original INDD into a new one and scale it that way.