How to sort List in Data Structure

Question

I need to create an algorithm in java that sorts a list, I've created the part where the list is made, but I can't sort it, I have tried to add bubble sort and merge sort but none of them worked, here is my code, I would really appreciate the help.

import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

class No{
    int number;
    No next;
    public No(int number){
        this.number = number;
    }
}    

class Lista{
  No head;
  public void add(int n){
    if(head == null){
        head = new No(n);
    }else{
        No temp = head;
        while(temp.next != null){
            temp = temp.next;
        }
        temp.next = new No(n);
    }
  }
  public String toString(){
    No temp = head;
    String str = "";
      while(temp != null){
          str += temp.number+" ";
          temp = temp.next;
      }
      return str;
     
  }
}```