There are a few different methods for moving ideas between forums and categories in UserVoice.
Bulk moving ideas1) In the suggestions grid, use the checkboxes to select multiple ideas you wish to move.
2) Click on "More actions" and choose "Move suggestions."
3) In the corresponding pop-up, you will see options to select a new category or forum to move the ideas to.
Moving individual ideasWhile you can use the above bulk method to move a single idea, there is another way to move a single idea between categories or forums.
1) On an idea, click the three dots and choose "Edit."
2) From the pop-up, you will see corresponding drop-down options to change the forum or category of the idea. Change these, and click "Save changes" to move the idea.
Moving ideas (legacy interface)Similar to the above, in Legacy UserVoice if you edit an idea you can move it to a new forum or category.
Additionally, you can bulk move all ideas in one forum to another (but not between categories within a forum). In the feedback section, click the "gear" icon in the upper right next to the "Add idea..." button