Open the sheet you want to add the render to.

Select the "Add Image from Various Sources" tool in your toolbar and the modal will open up where you can select the "Render" section.

All the renders that have been taken in this design file will be shown there and you can select which render you want to add by clicking on the same. Place it in the sheet as required.

Select the render and the properties like size, transparency, orientation will appear in your design panel on the left side. You can make any changes you want there.