PHP Manual: Sets the date

Object-oriented style

public DateTime DateTime::setDate(int $year, int $month, int $day)

Procedural style

DateTime date_date_set(
    DateTime $object,
    int $year,
    int $month,
    int $day
)

Resets the current date of the DateTime object to a different date.

Like DateTimeImmutable::setDate but works with DateTime, and changes the existing object.

The procedural version takes the DateTime object as its first argument.

object: Procedural style only: A DateTime object returned by date_create. The function modifies this object.
year: Year of the date.
month: Month of the date.
day: Day of the date.

Returns the modified DateTime object for method chaining.

DateTime::setDate