First add a Post-process Volume to your scene:
Navigate to the “Modes” panel in the upper right and search for “Post Process Volume”. Click and drag the item into your 3D viewport.
Next, in the properties panel on the right, search for “Infinite Extent” in the search bar. Make sure this setting is checked as seen below.
All post processing effects can be found under the properties panel of your Post Processing Volume:
You can find more information on all effects at the Unreal Docs.