Bloodline Help

Hi, first sorry if already someone put this question but i can´t see.
Someone tell me how i get a bloodline for my house if i dont have.

for example i start a game in Aegon conquest and greyjoy house dont have a bloodline. Now i see that someone in dinasty have forge a bloodline in greyjoy house that grant a claim in iron islands.

my question is,, how can i do that in one house that dont have this type of bloodline.

thanks