Please refer this link on how to automate seek bar.
You can also use the following code to automate seek bar
WebElement seekBar = driver.findElement(By.id("com.cj.scrolling:id/seekbar"));
//Get start point of seekbar.
int startX = seekBar.getLocation().getX();
System.out.println(startX);
//Get end point of seekbar.
int endX = seekBar.getSize().getWidth();
System.out.println(endX);
//Get vertical location of seekbar.
int yAxis = seekBar.getLocation().getY();
//Set slidebar move to position.
// this number is calculated based on (offset + 3/4width)
int moveToXDirectionAt = 1000 + startX;
System.out.println("Moving seek bar at " + moveToXDirectionAt+" In X direction.");
//Moving seekbar using TouchAction class.
TouchAction act=new TouchAction(driver);
act.longPress(startX,yAxis).moveTo(moveToXDirectionAt,yAxis).release().perform();