Congratulations on the new H90! There are many ways you can set things up, depending on what you want to accomplish.
I would start simple, put the H90 either before or after the Helix (stereo or mono depending on your setup) so you can get an idea of what effects you like on the H90 and how it works.
You could also use Dual Mode on the H90, using the send/return paths from the Helix to have two different effects paths: https://cdn.eventideaudio.com/manuals/h90/1.7.1/content/edit-modes/routing.html#dual-routing
Or you could do a pre/post 4CM setup: https://cdn.eventideaudio.com/manuals/h90/1.7.1/content/setup/pre-post.html
There are many variations on how these devices can work together. If you have something specific that you’d like to accomplish, I can recommend more specific instructions. Start simple and try not to overthink things.
I would highly suggest watching our tutorials in the meantime: https://www.youtube.com/playlist?list=PLhT2MsSeKiDy8WEtcIYqmvOVaKCe-bEdf
