Give it time and space, without distractions. If that does not work do take distractions, and from time to time ask yourself: could this help me? How could this apply to something, or help me with a trail of thoughts?
By thinking of other games and concepts I already have a few ideas I want to explore.
This is a matter of creativity. If you are/were not trained in that area (which you absolutely can change in the long term) you can also consider joining up in a team and contributing that way. Let someone else do the creativity and designing, and maybe contribute some ideas to an otherwise established concept or topic. Or none of the sort, but contribute in a more technical and practical way.