How To Add Business Partner To Lex Bots In IAM?

I added him as a user in IAM Identity Center, but in IAM Dashboard, he doesn't show up. How do I change permissions and policies so that he can access and help me work on the Lex bots together? Do I have to create a user profile for him again in IAM Dashboard, or can I migrate him over? I asked ChatGPT, and usually it can help me with these kinds of stuff, but even it's confused as to what to do. And if it helps, the Lex bots are still just drafts, they haven't been built nor deployed yet.

I do see permissions and policies for IAM Dashboard, but not in IAM Identity Center; I'm new to all this, so I don't really know how any of thos works. I've tinkered around with IAM Identity Center, and so far I have only added my business partner as a user, created a group, and created a permission set using one of the defaults System Administrator. I only want him and future partners to my startup to have access to everything necessary for developing and deploying apps, but not access to permissions, groups, roles, billing, etc.

UPDATE: Ok I asked Bing AI, and it told me that the IAM Dashboard is completely irrelevant for my needs, and also I am to continue configuring the permission sets to allow him to access and work on the Lex bots with me.

UPDATE 2: Seems Bing AI is kind of gaslighting me, but I've managed to successfully provision the permission set so my business partner should have access to the Lex bots now. I added SystemAdministrator and AmazonLexFullAccess policies to the permission set, and I somehow made my account appear in the list, which my partner is a user in IAM Identity Center. I also remembered to enable Asia Pacific Hong Kong region, since that's where he's located and maybe that's partially causing him to be unable to view anything I'm working on.