IAS tenant administration in Free Tier BTP

Hi,

I'm using Free Tier BTP and would like to play around with IAS. Therefore I need my own IAS tenant.
What's the way to create it?

On HANA Academy I saw a video in which they told to "Establish Trust" in the Trust Configuration of a subaccount. When I click the button in my BTP cockpit I don't get a list of tenants. I gues it's because I'm using Free Tier.

Do I have to create a new IAS service instance in my subaccount and will I then be able to establish trust to my tenant or what else do I have to do?

I know that when I create a new IAS service instance I have to pay for it. It's no longer supplied as free service.
That's ok, but I'm not sure if this is the right way .

Thanks in advance
Helmut