update meta data

[arashnz]

Hello, Here is meta_value for a custom field https://0bin.net/paste/-n1daYYq#XduIwpuO0u+9Sf8fQzAVqJnso9oRwK+CwTZq+0ozhmc which I think created with option-tree, How can i add or update this field using add_post_meta ? i think its in a json format, but how can i create a new json containing title and al_url320 value ? is there any function for this ? I want to do it with php