The number one way to remove COR is checking the pool of water at the temple near the bull tribe and drinking from it. The pool can only remove up to a maximum of 100 COR but with the new pet slime event added in v0.27 you have a new and to my knowledge infinite way to remove COR
explore the areas that you normally find slimes in and you will find a baby slime that you can befriend (you must have at least returned from the snow mountains for the baby slime to appear)
For content
Stage 1 of slime development
There really isn't much to do you can choose to play or pet it. You can choose to feed it and the MC will feed it with cum (there isn't a scene just dialogue)
Stage 2 of slime development
If you explore some more you can find the pet slime again and if you have at least fed the slime I think 2-3 times during stage 1 the slime will appear more grown. If you have 40 or more lust you can "feed" it (have sex with it) unlocking the first sex scene
Stage 3 of slime development
After you "feed" the pet slime 3 times during stage 2 (having sex with the slime removes 10 COR) it shall grow bigger once you meet it again. If you have 40 or more lust you can "feed" it unlocking the second sex scene
Final Stage of slime development
After you "feed" the pet slime 3 times during stage 3 it shall grow even bigger once you meet it again. If you have 40 or more lust you can "feed" it unlocking the third and final sex scene.
"Feeding" the pet slime stage 2 and onwards will remove 10 COR with no apparent limit to how many times you can fuck it after reaching the Final Stage