Can you swim in saltwater 2 days after face microneedled wearing SPF of 50?

Yes.
It takes 48-hours for the skin to re-epithelialize (heal) after a microneedling treatment.

It is not recommended to swim in salt water, or any body of water for that matter, post-microneedling. Your skin will be exposed and should be treated very gently after the procedure. It takes the skin 48-hours to start the healing process, but we recommend staying out of swimming pools or salt water for at least 2 weeks, and absolutely avoid any sun exposure for 2 weeks (or indefinitely!).