That is right. We can consider the following analogy.
Most of us have not been to Africa. But do any of us have doubts about the existence of Africa?
– There is overwhelming indirect evidence for the existence of Africa.
It is the same with the existence of hell or Deva/Brahma realms.
– As one learns Buddha Dhamma, one will be able to verify by “indirect means” the validity of the existence of those realms.
– One needs to start getting rid of wrong views with basic concepts like kamma/kamma vipaka and rebirth. Just keep an open mind and look at the evidence.
– Such fundamental truths INEVITABLY lead to the conclusion of the existence of the 31 realms, gradually.