General aviation pilot reported a near miss with another aircraft during initial approach to PIE airport. The pilot identified the traffic on ADS-B; alerted ATC to the traffic; then initiated an immediate descent to avoid the conflict and told ATC the traffic had passed.

Narrative

We were in a Aircraft X on our way from ZZZ to St. Petersburg on an IFR flight plan. After we had planned an approach to Runway 18 at PIE and were already northwest of the airport; ATC advised us that the wind had shifted and we should now plan an ILS approach to Runway 36 for St. Petersburg. So we flew south again at 4000 feet. ATC instructed us to descend to 3000 feet and fly a heading of 130; we followed this instruction. We then noticed traffic on our ADS-B and advised ATC about that. After we were ignored at first; we alerted to ATC that we have traffic in sight and that it is a potential factor for us. From there; ATC asked us who had called. We told them that we were calling as Aircraft X and pointed out again that we have traffic in sight at 2 o'clock at the same altitude. ATC then instructed us to fly heading 090. We requested a lower altitude. To avoid a collision we initiated an immediate sharp descent before we were cleared down 2000 feet by ATC. This allowed us to avoid a mid air collision. We made ATC aware that this traffic has passed. ATC apologized.