There isn't really a way to 'remove' an alter so to speak. There's integration, which is where two alters or a host and alter will come together to create one whole, but that's usually done through many therapy sessions while working through past trauma.

alters are apart of the brain, they are a consciousness, and they cannot be removed. there is splitting, where a singular alter becomes multiple, and integration, where multiple alters become one. there is also dormancy, where alters essentially go into a deep sleep. otherwise it is possible to sort of reform alters, help them get better