breast to bottle but how ?

March🕉
I want introduce a bottle with my breastmilk to my 4 week old but she eats randomly now sometimes every 3 hours sometimes less and if she's awake then she's cluster feeding or just wants milk constantly. 
She empties my breast when she feed so I barely have any extra milk when I go pump after a feeding, even 1-2 hours after so then I just let her nurse again and never end up filling a bottle enough for her next meal. 
How do I switch completely from breast to bottle (pumped milk)  with her random feeding schedule ?