There was some weird moldy smell coming out from my lid no matter how much I cleaned it (my fault, I put milk tea in there, lesson learned, do not use the Contigo Fit / Chill for anything other than water). And I didn't want to buy a new lid, so I took it apart and cleaned it out.
Step 1: Unscrew Triangle Screws
If you have a triangle screwdriver then this'll be easy, but if you don't, don't worry. It still worked with a flat head, I used a 5/64" one from a cheap dollar store set. Be very careful and go slow, you don't want to strip the screw.
If it's not working, try adding a small flathead next to it and use both hands to turn the screw at the same time. (I did this at first and as I went along I figured out that I didn't need to do that)
Step 2: Open Up
Remove screws and gently pull apart the top and bottom. Be careful to not lose those little rings in the yellow part of the lid.
Step 3: Removing the Push Button
This part is the trickier part.
1. Tilt that little rectangle side piece so it's horizontal.
2. Push/Pull the black rubber gasket until it's sitting on top of the spring.
3. Push the assembly out as much as you can and pull at the spring area until the rectangle plastic pops out.
4. Pull the rectangle plastic, the spring, and rubber gasket out.
Step 4: Pull Out Metal Rings and Rubber Gasket
Pull out those 4 rings with a toothpick or tweezer. BE CAREFUL. They're tiny and thin, you can easily lose them.
This was the source of my moldy smell, somehow the liquid got in between all these.
Take out the rubber gasket too.
Step 5: Dismantled
Here's all the parts I took out.
I soaked the metal rings in vinegar but I couldn't completely make it shiny again. I'm guessing they're not stainless steel.
Clean very thoroughly with q-tips and stuff. There was gunk around the rubber gasket areas.
Step 6: Reassembly
1. Push in the autoseal button.
2. Put in rubber gasket, do not put it back in the tab yet.
3. Slide on spring and rectangle plastic.
4. Try to shove it all in there.
5. Move rectangle piece so it's vertical. Test out the button.
6. Place rings back onto the lid.
7.. Gently reassemble the lid. Make sure to have the yellow side down so the rings don't fall out.
8. Screw back in.
And you're done!