Bump a thread, without making a post. Just click on "Bump". Done.
Bump is positioned on the thread tools.
Only the users that you give permissions can bump the thread. Either give the permission to a usergroup, or give it to a moderator on that particular forum, or create User Permissions for a person in the forum.
You have the following options
Set the time limit that the users must wait before bumping another thread
Setting the max number of threads that can be bumped under that time period