In this method, first node in the doubly linked list with specified key (value) is deleted. For example - if the given List is 10->20->30->10->20 and the first occurrence of 20 is deleted, the List becomes 10->30->10->20.

First, the head of the doubly linked list is checked for null value. If the head is not null and the value stored in it is equal to the key, make head next as head, delete previous head, and adjust previous of head. Else, traverse to the node previous to the node with value equal to key, and adjust links.

The function pop_first is created for this purpose. It is a 3-step process.

```void pop_first(int key) {
//1. check if the head is not null
if(temp != null) {

if(temp.data == key) {
nodeToDelete = null;
} else {

//3. Else, traverse to the node previous to the
while(temp.next != null) {
if(temp.next.data == key) {
Node nodeToDelete = temp.next;
temp.next = temp.next.next;
if(temp.next != null)
temp.next.prev = temp;
nodeToDelete = null;
break;
}
temp = temp.next;
}
}
}
}
```

The below is a complete program that uses above discussed concept to delete first occurrence of the specified key (if exists) of the doubly linked list.

```//node structure
class Node {
int data;
Node next;
Node prev;
};

}

//Add new element at the end of the list
void push_back(int newElement) {
Node newNode = new Node();
newNode.data = newElement;
newNode.next = null;
newNode.prev = null;
} else {
Node temp = new Node();
while(temp.next != null)
temp = temp.next;
temp.next = newNode;
newNode.prev = temp;
}
}

//Delete first node by key
void pop_first(int key) {
if(temp != null) {
if(temp.data == key) {
nodeToDelete = null;
} else {
while(temp.next != null) {
if(temp.next.data == key) {
Node nodeToDelete = temp.next;
temp.next = temp.next.next;
if(temp.next != null)
temp.next.prev = temp;
nodeToDelete = null;
break;
}
temp = temp.next;
}
}
}
}

//display the content of the list
void PrintList() {
Node temp = new Node();
if(temp != null) {
System.out.print("The list contains: ");
while(temp != null) {
System.out.print(temp.data + " ");
temp = temp.next;
}
System.out.println();
} else {
System.out.println("The list is empty.");
}
}
};

// test the code
public class Implementation {
public static void main(String[] args) {

//Add five elements at the end of the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.push_back(10);
MyList.push_back(20);
MyList.PrintList();

//Delete the first occurrence of 20
MyList.pop_first(20);
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10 20
```

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