first you have to make the opponent faint, and then when it says go back to map you dont click it. Instead you refresh the page. The pokemon that your willing to catch should have 0/hp from here you cant use any attack or else it will automatically faint.(usually players want to use paralysing attacks or attack that weaken the pokemon)
You use a pokeball or any other ball(besides the master ball or else then you wouldnt have to do this cause it already has a high chance)and then it should have a higher chance, im not saying that this is a definite. But it should work.
please dont hate on me if it doesnt work.