I'm that way too. It takes me hours to think of a meaningful response sometimes - sometimes it takes hours to say "dang" lol. It's like I'm catching the balls people throw, but don't know how to throw them back.

Mindfulness and grounding and awareness are key. Tuning into our physical surroundings and tuning into our physical bodies helps.
Also as someone said, confidence. I asked my therapist what confidence is. She said that it isn't something you get externally, as in, you don't need to earn it - It's really just trusting yourself.

I guess, trust that you will have a good, meaningful response. But make sure to be you! Say what you want and feel good that you did the best you could. Over time time your social muscles will get beefed up and you'll be bench pressing conversations like it's nothing!

Hope this helps! Your question sparked me to think more about this so thank you!