change json column to many to many relation without losing data

i am working on a project with laravel (doctrine orm)

i have a table named posts

posts table has a json column named tags,
every post’s tags stored in their json column

im trying to change it to a many to many relationship.

Problem: i need to have same tags in my new structure. and i don’t know what is the best way to do this change and store all of my json tags in my posts_tags table.

Note: my problem is not about changing the structure, its about having same data after this change.