Help with ECs

Hey guys ! I am an asian female . I am currently starting As level or 11 grade but i need help with ecs as my school didnt provide any except for debates at all . It is to be noted that my school was very competitive in terms of grades but provided no help in ecs. I am from south asia and want to apply in t20s and cambridge with major in cs . Can you guys please suggest me some probably online ecs regarding this . Thanks in advance 💫