#1. let's define a date with format Y-m-d
$date = "2022-01-03";
#2. what we want is to add a number of days from initial date and get the new date.
# 2.1 convert initial date with carbon
$c_init_date = CarbonCarbon::createFromFormat('Y-m-d', $e_join_date);
# 2.2 add number of days from $c_init_date. let's say 7 days
$new_date = $carbon_now->addDays(7)->format("Y-m-d");
#3. the result must be "2022-01-10"
die($new_date);