I've got an external device that uses a small app to update firmware, however it needs me to add a file to the folder indicated above.

It is a root account folder so I need to temporarily access it to add the file.

How can I do this?
Thanks

With su or sudo

See:
man su
man sudo

Thanks, but tbh, that doesn't mean that much to me?? Well, I know what SUDO is and I have used it many times for various task, but changing the permissions for a root folder is not something I have looked at before. I assume changing the permissions is the way to go on this?

How do I apply that to open the folder and allow a file to be placed in it? Where and how do I run that command (if it is a command?)

it looks like you do not really understand how does it work. Only the user root has right to place a file into that folder. So you need to use either su or sudo to change the current user to root [to be able to do that].
You do not need to change the permission of any folder.

And you shouldn't change the permissions or ownership of system folders anyway. They are the way they are for a reason.

Yes I already know that! But you folks seem to post instructions as if people asking were already experts in Linux!! And if that were the case, we wouldn't be asking questions!

All I want to do is insert a simple text file into that folder.....sheesh! this is like extracting hens teeth! No offence meant but tbh, folks need to understand that not everyone new to linux is an expert! Please try to remember YOU were once a novice.

I ask a simple question, and I get some cryptic reply, then one saying I really don't understand (well, and no offence, but duh! that's WHY I'm asking) and then the last saying that permissions are there for a reason. None of these even remotely go to an answer to the OP.

I have found how to get to root in the terminal, which is all fine, but that gets me no closer to how to add a text file to that folder. Do I run nano in that root terminal? Can I run a text editor outside the terminal?

I'll probably get upbraided now for "attitude"!

What file manager are you using? This works in some, like thunar... Type (or paste) the following into the address bar:
admin:///etc/rules/udev.d
Yes, three slashes. You can also start at root and click you way there from:
admin:///

You'll be prompted for password twice.

Alternatively, you can use sudo from terminal to launch an editor, sure. like
sudo nano /etc/rules/udev.d/newfile

You'll be prompted for password once.

Issue is solved. I installed Nautilus as the file explorer and ran it as root. DuckDuckGo gave me the answer. It's a shame the "dedicated" EOS forum couldn't

Thanks for that, I appreciate the reply and the hint! See above I managed to sort it going a different way. But I WILL put that line in my linux tips file

You can definitely tell us you don't understand the answer, and we will try to give you better answers. From my side it is ok.
Actually we have no any idea about your practice, knowledge, so sometimes yes, not that easy to give the correct answer.
So please try to understand. It looks like you know how to be root, so at least the first step is ok.
You can definitely use nano, if you wish, or you can use your favorite text editor. You can also run a text editor outside, but based on your answers would be better to use nano - to add that file to the folder indicated above.

@pan64 thanks for the reply. Seems you do understand

As I wrote above, I finally got it sorted out via an external method. So I'll mark it as solved.

cheers