You should add the same amount as your original position to each trade. BUT remember adding to positions is an advanced technique.
So master the basics first.
Also adding to positions is a trade off. It means a few very big profitable trades, in exchange for giving up some small ones which were in profit at a small level, but you added to them and risked your profits for more profits and they may then turn back into breakeven.
So would you rather have more winning trades with small profits or more profits but fewer (small) wins. All trading is a tradeoff.