Advice desperately needed for this branch of an apple tree from my childhood home

Hi Reddit. Today I said goodbye to my childhood home. I managed to get hold of a branch of the cooking-apple tree at the bottom of the garden before we left, and I want to propogate it as a keep-sake. The terms of losing this home has been quite heartbreaking, so it means a lot to me to keep this branch alive. What is the best way of doing this in British summer time? Thanks!