Here's some ideas that might help.
First of all, if you are a planner, then perhaps write without plans and see where your writing takes you. Now if you are a panster, do the opposite by creating several endings and pick your favorite.
Here's a few ideas on how to end your story:
1. Plot Twist - you know how this works and talk about an exciting ending! Just make sure to give readers a few hints along the way.
2. Tie the story back to the beginning. One of my friends wrote a fan fiction piece where she ended the story with a letter that was revealed earlier in the story. It was a pretty fun and clever ending!
3. The resolved ending where everything comes together neatly.
4. The unresolved ending which is good for those planning to write a series.
And if all else fails, maybe you just need some feedback. Take your WIP to someone you trust and use them as a sounding board. That might be all it takes to jump start you back into writing.
Here's a to a happy ending!!