I have a table
id_user | fname_user | lname_user | blood_group | date_donate | state
i want to set dynamic change (every day) of state to => 'available' only if
(currentdate) - (date_donate)= 3 months
You typically use a script or application to do this. I would check machine and config times are how you want them, write a script then add it to a cron if Linux or OSX or something like task scheduler if Windows. You can also look into the AT command for Windows.