That can be a hard enough conversation to have even if they know. Being straight up rejected by some high percentage of people who started to chat you up and are done the minute you mention HIV would be a dreadful experience. It's possible they are on the app precisely for the ability to pre-screen people for their willingness to hook up with someone HIV positive.
A) Mark yourself as HIV positive in your profile, which Grindr will share with third parties.
B) Directly declare yourself as HIV-positive at some point in a conversation.
I’m not suggesting there are options without drawbacks.
Its not even clear if whats being sent to the analytical companies is whats displayed in the profile or all fields even if they are not displayed.