Something like this:

https://smile.amazon.com/gp/product/B0017OLHNM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

But I've also purchased in the art dept at Michaels.

I have a very small spray bottle (came in a 3 pack at Michael's or Hobby Lobby) that I use for larger jobs, but I also have a water brush that I use for smaller corrections. It's got a very fine point so it's easy to moisten a small area. I believe they have those in the craft stores too, in the art supply/drawing area but I got mine on Amazon. (https://smile.amazon.com/gp/product/B0017OLHNM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1)