Malicious allegations at work

Good day. My friend is having a problem at work. Her officemate is accusing him of touching her sensitive body parts when they watched a movie last time. This girl was the one who invited him to watch the movie and he just slept at the theater house bacause he does not really wanted to watch movie. Then just a few days ago, the girl is spreading humors that she was abused and touched by my friend during at work. She was also pinpointing two other staffs that were abused, but these staffs have reiterated that nothing has hapeened to them. She even contacted previous staff (whom the girl has never met) and asked her to accuse my friend of the same allegations as her, but the previous staff did not agree because my friend really did not do anything wrong to her. In a meeting called upon by their superiors, the girl admitted that she is only making falso accusations to my friend because she wanted a higher position. An amicable settlement was agreed upon that the girl will be provided with higher position but she must follow the proper application process. If she does not pass the interviews and training, no one shall be blame. However, after another day, the accusing girl went to their head office and still accusing my friend. Both of them were laid off by the company until the case was unresolved.
Since this has cause too much wreck on the side of my friend, for his reputation and dignity, he wanted to take some legal actions. What should the process be?
Thanks in advance for answering!