Tenants have split on bad terms - how do I revise the lease?

A while ago I rented my small unit out to 2 girls, and both signed the lease. Just recently, the girls had a falling out and one of them has given me her 30 day notice to exit - the other is intending to stay on her own. The girl leaving has also requested for her name to be erased from the lease, as understandably she does not want to be held liable for any potential damage the remaining girl accrues. While I’ve only had a few tenants in the past, this is a completely new situation for me. That being said, how would you suggest I go about revising the lease and what kind of documentation should I send over that would acknowledge the exiting girl’s departure and the remaining girl’s continuous lease? Thank you in advance.