Everyone grumbles about the administrative tasks at work - filling out timesheets, expense reports, etc. It's usually the last thing we do because we've been putting it all off because we know how horrible it is.
I'm not going to tell you to do it first, but I am going to tell you two key things:
Realize it IS important - just not to you.
Never grumble about it or accept grumbling from your team.
First, importance, much like beauty, is in the eye of the beholder. I happen to think watching baseball is important. My wife and daughters - not so much. Same with these admin tasks. They may feel like a burden to you, but someone needs it and is thankful you do it.
I will say, running my own business of one now, I have to do all these things myself. I've found doing the admin tasks may not be important when I do them, but when I need to fill out my taxes, they are critical and I'm glad I organize it the way I do. It doesn't mean that the person who eventually gets the admin information doesn't need to try and make it as easy as possible for you, just realize that it is always more complicated than you think.
Second, grumbling from your team may be harmless venting. Do not accept it as fact though. Challenge them like I did with you above. Ask them - do you think this isn't helpful to someone? If they don't know, challenge them to find out.
I know some managers who like to let the grumbling proceed and then agree with them - it makes them seem relatable and part of the team. I know I used to do that. But it hurts the overall culture. It makes certain departments or functions seem less "worthy" of your support.
If nothing else remember this - that annoying expense report form ensures the bills get paid and the lights stay on. And also that you get paid.