I think that you'll not find any kind of 2019 Vista 27PE-specific diagrams, plans and how tos.
Each person is pretty much on their own because of the subtle differences between everyone's specific RV.
When I made my conversion in 2022 for my 2017 Adventurer I found great general info... mostly at www.irv2.com
but no specific Adventurer info. Certainly not for my model year.
I posted a number of diagrams... all of them turned out to be incorrect until I stumbled on the correct way - for me - to complete the project.
There are dozens of general Lithium upgrade posts on irv2.com and videos on YouTube to get you started.
Best of luck in your project. It's not that difficult but it does require ton's of research on your part and a complete understanding of the electrical system of your motorhome.
Here's a link to your 2019 Vista 27PE wiring diagrams - there are two versions based on your serial number:
29VE (Serial Number begins with 10E40Y1)
29VE (Serial Number begins with 10E40Y2)