Updating string in mysql

Hi everybody. I have a string be save in mysql database. When i var_dump it like this.
string(280) “{“2016-01-07”:{“available”:”3″,”bind”:”0″,”price”:”1000000″,”promo”:”0″,”status”:”available”},”2016-01-08″:{“available”:”3″,”bind”:”0″,”price”:”1000000″,”promo”:”0″,”status”:”available”},”2016-01-09″:{“available”:”3″,”bind”:”0″,”price”:”1000000″,”promo”:”0″,”status”:”available”}}”
I want to update “available”:”3″ become “available”:”2″
Note: number “3” is not a constants. It is a variables when I query from database.
Thanks you.
Sorry my english so bad.