Basically it goes like this:
Causes and effects exists, therefore, there is a causal chain (i.e a chicken laying an egg, then the egg growing into a chicken etc)
However, something cannot cause itself (this was in the first way as well which you agreed to)
However, there cannot be an infinite chain of causality. Why:
P1 In order to have gotten to this point, we would've had to have successfully traversed the prior causal chain
p2 However, traversing infinity is impossible
p3 Therefore, the causal chain is fininte, and at the bottom of the causal chain there is something uncaused which caused everything to come into being
