Our glue gun holder has a metal cup so that the glue gun can rest into, but over time, the dripping glue has been accumulated at the bottom of the cup and got dried there, and really gets hard to remove it.
We basically heated up the bottom of the metal cup with a heat gun. The heat made the glue soften, then we carefully scraped the glue with a putty knife. I never thought of using a heat gun to melt the dried glue, but it is a great idea to get rid of the old dried gunk.
With the same technique, you can also fix some hot glue mistakes!