Show that if $T$ is not $\aleph_0$-categorical then $T$ has a non-atomic model of size $\aleph_1$

Question

Exactly as the title stated:

Show that if $T$ is not $\aleph_0$-categorical then $T$ has a non-atomic model of size $\aleph_1$

Would like some pointers on how to proceed.

Answer 1

Assume the language is countable. Then any non $\aleph_0$-categorical theory has a countable model $M$ that is not prime, hence not atomic. Let $a\in M$ realize a non isolated type (over $\varnothing$). Than every elementary extension of $M$ containing $a$ also realizes the same type.

I do not the answer for uncountable languages.