how can I change only year in date String?

java.time

You do not have to split the string and then combine the parts. You can parse the whole string into LocalDateTime and then use LocalDateTime#withYear to get a new instance with the specified year.

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class Main {
    public static void main(String[] args) {
        String creationDateTime = "2020-1-2 13:48:21";
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("uuuu-M-d H:m:s", Locale.ENGLISH);
        LocalDateTime ldt = LocalDateTime.parse(creationDateTime, dtf);
        System.out.println(ldt);
        ldt = ldt.withYear(2021);

        // Default format
        String updatedDateTime = ldt.toString();
        System.out.println(updatedDateTime);

        // Custom format
        updatedDateTime = ldt.format(dtf);
        System.out.println(updatedDateTime);
    }
}

Output:

2020-01-02T13:48:21
2021-01-02T13:48:21
2021-1-2 13:48:21

Learn more about java.time API from Trail: Date Time.

try:

String[] arrOfStr = parts1[1].split("-", 2); 

arrOfStr[0] contains the year

Now you need to parse it as an int (since it's only 4 digits)

int year = Integer.parseInt(arrOfStr[0]);  

year now contains the the number 2020.

you can do

year++;

to increase it's value by 1

and to put it back in String format do:

arrOfStr[0] = "" + year;

or

arrOfStr[0] = String.valueOf(year);

to put it all together do this

parts1[1]= arrOfStr[0] + "-" arrOfStr[1]; //  2021-1-2

finally it should look like this:

parts1[1]=   2020-1-2;
parts1[2]=   13:48:21;

String[] arrOfStr = parts1[1].split("-", 2); 
int year = Integer.parseInt(arrOfStr[0]);  
year++;
arrOfStr[0] = "" + year;
parts1[1]= arrOfStr[0] + "-" + arrOfStr[1];


CreatedDate = parts1[1]+" "+parts1[2];   
System.out.println(CreatedDate);