I created a wiki but then realized that there was another wiki about the same topic.
[Title edited by CrazyForMyself to make it clearer]
What do I do?
Just contribute to the existing wiki. Fandom will find and delete yours eventually. If, for some reason, you want it deleted sooner rather than later, you can submit a closure request for your wiki.
If you can think of a similar topic that FANDOM might not consider a duplicate you can also ask them to change the subdomain/name.
What do you think?