How to change image to delete the substrate color so that when prints colors look more correct

Are you trying to make the colour look different in the Photoshop window or when printed on the fabric itself?

Dave

To enhance the colors on your blue fabric when printing in red, consider adjusting the color balance and saturation levels in your image editing software. Increasing the saturation of red tones and adjusting the hue can help make the reds appear more vibrant without affecting the blue background too much. Additionally, adjusting the contrast and brightness settings can also help bring out the desired colors more accurately. Experiment with these adjustments until you achieve the desired outcome.