There are lots of resources online, for example bigclives videos.
This is the gist:
Depends on the kind of model, but usually you have two caps one one tube. If you take the one opposite to the mouthpiece out with a pair of plyers, you can usually slide the electronics out. Cut the wire at the battery and there you go. Just be careful: they usually are the pouch type, wich means its not that hard to squish, puncture or bend them, which might anger the spicy chemicals inside enough to have it ignite. Put them in the little plastic containers for photigraphic film rolls, pills, or something else rigid. Usually they have solder tabs that you can poke through the lid and bottom to connect to them. You can also solder some wire to these tabs instead.
Make sure to always follow safety precautiobs for small lithium cells, for example not heating it above 50°C. You might also want to add a cheap single li-ion cell protection PCB
You can repurpose them for low-power applications like wireless sensors. If you need more capacity, solder them in parallel, after making sure they are at the same voltage ±0.1V