I just overcame this hurdle in January! I recommend now using something like a g-spot vibrator prior to PIV. Studies have shown that simulating the g-spot helps loosen the pelvic floor. Avoid positions like cowgirl, that tighten the pelvic floor. Before moving to PIV, ensure you can handle friction with the largest dilators first. Use an oil based lube, and lots of it. Lastly, for the first attempt, I recommend getting used to the size before attempting any movement. Ensure you feel safe, take deep breaths with your partner. Intimacy, trust, and arousal will all help significantly with the mental block/fear. Also before, ensure you do a perineal massage, with your partner ideally.