Go to the coffee shop and chat up anyone you see that seems open to chatting with you. That’s how I did it.
Have lots of conversations with people you aren’t romantically interested in also, don’t just beeline for the ladies. They’ll smell the desperation on you like cheap cologne.
I’m not gonna lie, it takes a long time to develop those kinds of social skills. But you should take heart, finding casual relationships these days is way easier than finding serious ones.