Switch between two worlds ingame:

The 0 (Zero)-key held together with "page up" key will change to the other side. With 0 (Zero)-key held together with "page down" you will return.
 I mapped those key combinations to "mouse 4" and "mouse 5" buttons on my Logitech mouse (using Logitech hub). Anyone could e.g. use:  https://support.microsoft.com/en-us/topic/mouse-and-keyboard-center-download-f5b1 to do so (or similar).

Installation instructions
1) Please do the installation of Otherside itself manually and place all the files from the unzipped Otherside ENB directory, including its subdirectories, into your Skyrim install folder, where the SkyrimLauncher.exe is located. In the end you should e.g. find enbseries.ini file and enbseries folder in the same directory as SkyrimLauncher.exe. Make sure you have deleted any files from previous ENB intallations beforehand.

2) Additionally please download the newest ENB series (at the making of Otherside this was version 0.466) by Boris Vorontsov, from: ENB Dev (click "NEWS" to get deeper into the page and to downloads for Skyrim SE eventually). After unzipping this archive, go into its WrapperVersion subdirectory and ONLY copy the file named d3d11.dll and d3dcompiler_46e.dll.. Place these two files into your Skyrim directory, too. Only these two files are needed from the WrapperVersion, the rest comes with the Otherside files you downloaded in step 1 above.

3) For the followings steps 4 to 6 (installation of required mods) I use Mod Organizer 2 as my mod manager. You can use any other mod manager, too, though.

4) Also, please get the Skyrim Particle Fix from http://www.enbdev.com: Skyrim Particle Patch. Choose the version for the Legendary Edition (and not Oldrim). 

5) I  advise downloading and activating Lux and Lux Orbis mods by GGUnit (without them you might have a different look than intended, though worth a try). I use their standard versions (no brightness adjustments). When installing Lux make sure to choose the Beams and Fogs for PARTICLES options as well as the Webs option. Lux mods in turn require the unofficial Skyrim Patch Mods (Normal and for Creation Club Content). Optionally, I recommend using Rudy's "More lights for ENB" series of great mods that add ENB additional complex fire light (aka glow) to various plants, creatures and objects in Skyrim.

6) Mod Load order (you can likely mix the last two as you like, it's just my current set up):
Unofficial Patches
Skyrim Particle Patch
Lux Orbis
Lux 

7)Sykrimprefs.ini
Please make sure that in your Skyrimprefs.ini you have the following set:
bTreesReceiveShadows=1
bDrawLandShadows=1
bUse64bitsHDRRenderTarget=1

8) Ingame graphic settings (launcher and options menu)
I have brightness slider in the middle (adjust as you need). Also I use TAA for anti-aliasing. DOF is turned off here (Otherside will deactivate it anyway though and use the included Matso Bokeh DOF instead).

Credits
Boris Vorontsov for creating ENB in the first place (and further developing for over a decade, wow)
GGUnit for Lux and Lux Orbis, which are so masterfully done
Matso (MartyMcFly) for the brilliant Bokeh DOF
Mindflux for Skyrim Particles Patch
Rudy for the Further Lights for ENB series which adds so much flavor to the game
Arthmoor and the great Unofficial Patches team
All you fellow ENB makers who have been in this same rabbit hole :-)
Bethesda, of course (go, Starfield, go!)