We have 100 mL of $0.1 \mathrm{M} \mathrm{KCl}$solution. To make it 0.2M:

$100\times 0.1=0.2\times V\Rightarrow V=50 \mathrm{mL}$

So, volume of solution should decrease by 50 mL without decreasing quantity of KCI. By adding $0.01 \mathrm{mol} \mathrm{KCl},$ Total moles $= 0.02$

$\Rightarrow \mathrm{KCl}\text{ solution }\to 0.2\mathrm{M}$