Put 1/4 cup baking soda in the jar. Add 1/4 cup of lemon juice or white vinegar. The vinegar will do a great job, BUT combining it with baking soda will cause it to bubble up. (Kids use baking soda and vinegar to create 'lava' for 'volcanoes' in school projects.)
Fill the jar with HOT water. Shake well to dissolve baking soda. Put the lid on tightly. Turn it upside down in your kitchen sink to be sure the lid is immersed in the soak solution. Let it soak overnight.
I've had great results getting odors (and stains) out of dishes (even Tupperware and Rubbermaid containers) by doing that.
If that doesn't get the smell of salsa out, I would wash the salsa lid in the dishwasher, if you have a covered silverware basket. The cover would hold it down and the strong d/w detergent would most likely get the smell out.
Hope this helps!