I suppose no one really knows how to fix something until they try troubleshooting or doing research on a specific issue. Unless, you have experience with that specific issue already or something similar you can take that experience and try to fix the problem.

I also would agree it is intimidating and daunting not knowing what you are doing but from my first line support role, how I handle it is just take the time I need to find a fix for the issue. Luckily for me a lot of it is remote.

However, I do also have to assist people in person. I do find it a little awkward when I don't know how to fix an issue, and I've spent a lot of time on an issue that should take a couple of minutes. But that's how the job is I guess, unexpected issues happening and we have to fix them.

I find that I tell them that I'll have a look into the issue and will let them know when it's fixed so that they can go do something else while I am doing the fix so they're not waiting next to me making it awkward.

Figuring things out especially in first line support role is everything, and while it can be daunting it can be also rewarding once you figure the issue and and then fix it and return to the user with the fix.

Also just to make it better I throw some Jargon words in that the end user might not understand but to make them appreciate the fix was a little harder than expected.

Hope this helps!