Rebble have an official official guide based on this, so please follow their guide on their website at help.rebble.io/sideload-ios-app.
Please direct your questions and suggestions to the helpful people in the official Rebble Discord Server
This guide is in maintenance mode. I am only keeping this guide up as a archive and for those who stumble upon it through old links.
Thank you for all the support, and long live Pebble and Rebble!