Unroot of cell phone not possible, because according to SuperSU supposedly no root exists, what to do?

The question is already as good as above, here are a few details.

And I want my Huawei P8 lite unrooted with SuperSU, but this shows me constantly that the phone is not rooted, but all RootChecker apps already. Repeated reinstallation of SuperSU and restarting the phone has brought nothing.

What can I do?

New firmware on it

Easier said than done ^^ *

Have done many times, download, odin open (while mobile phone in the downlaod mode) with odin the new firmware on it and ready. So it was with me

So right now the newest firmware should already be on it, what should I do then? ^^

On the internet the predecessor get or try to make the latest trozdem on it

I'm afraid of a brick, but you can try it

Okay okay ^^

If you already have european firmware (ale-l21) you can follow the instructions here

https://www.carbontesla.com/2018/04/download-huawei-p8-lite-b636-marshmallow-update-europe-dual-sim/