Separating Apple ID at Retirement

I am retiring in several months and my employer required me to use an AppleID on my phone that is my work email so it was on our work server for security. My work and personal Apple ID were merged without my consent when everyone was forced to go to the one ID. I need to separate because my work ID and email will be deleted after I retire. what is the best way to go about this with retaining as much personal data as possible?