To sort scrips in your desired watchlist, click on the 3 dots beside the Watchlist name and you will get a pop up menu.
This menu contains 5 ways by which you can sort your scrips.
For Manual sorting, you can click on the ‘Manual Sort’ button beside Sort By or you can also long press on any stock in a particular watchlist.
This will open a screen where you can drag & drop the scrips by clicking on the drag icon beside the name of the scrip.
After you are done re-arranging the scrips, click on save changes.
Now, your scrips will be sorted manually.