A file that looks fine on screen can print blurry. The reason is almost always resolution: not enough pixels for the size you want to print.
Pixels are the real detail in the image. DPI only says how many of those pixels go into each inch of paper. Print size = pixels ÷ DPI.
300 DPI is the standard for flyers, cards and photos. Large banners seen from far away can use 100–150 DPI. A4 at 300 DPI needs 2480 × 3508 pixels.
Raising the DPI number alone makes the print smaller. Use the HD Upscale tool to add real pixels with AI, up to 4x, then export at 300 DPI.
Check the pixel size, export at 300 DPI, use CMYK if the print shop asks for it and keep important text away from the edges.