The print comes back and it is darker, flatter and slightly warmer than the picture on your screen. Nothing went wrong at the lab. A monitor emits light and can show a white brighter than any paper; a print can only reflect the light in the room. The gap is physics, and the job is to edit on a screen that behaves more like paper.
Turn the brightness down
Most monitors ship at or near full brightness, which is right for a bright office and wrong for judging a print. Bring it down until a white document on screen looks about as bright as a sheet of paper held next to it in the same room. On a typical monitor that is somewhere around a third to a half of maximum. Your photos will suddenly look darker on screen. That is the point: now you will brighten them while editing, and the print will come back the way you saw it.
Work in sRGB and embed the profile
Consumer print services expect sRGB. If your camera or editor is set to Adobe RGB, the file has a wider range of colours than the service will use, and the conversion at their end flattens saturated reds and greens. Set the export to sRGB and tick the box that embeds the profile, so the service knows what it has received. If the software has no such box, it is almost certainly exporting sRGB already.
Soft-proof when the lab gives you a profile
Some labs publish ICC profiles for their papers, Saal Digital among them. Load the profile in your editor’s soft-proof view and the screen simulates that paper: the white point drops, the blacks lift, saturated colours that the paper cannot reproduce are shown as they will print. Turn on the gamut warning and any colour it flags is one the paper will dull. It takes two minutes per image and removes most surprises. If your editor has no soft-proof, Affinity and DxO PhotoLab both do.
Judge the print in daylight
A print looked at under a warm living-room lamp in the evening will look warm and dull, and the same print by a window at midday will look like the file. Judge prints in daylight, or under a neutral white lamp, before deciding the lab got it wrong.
When a calibration device is worth it
If you print more than a few times a year, or you sell prints, a hardware calibrator (a small sensor that hangs on the screen) sets the monitor’s brightness, white point and colour response to a known standard and writes a profile. It is the difference between guessing and knowing, and it costs less than two large prints that came back wrong. For everyone else, the brightness setting above gets you most of the way.
The order of operations
Lower the brightness first, edit second, soft-proof if the lab offers a profile, export sRGB with the profile embedded, and judge the result in daylight. Do it in that order once and the difference between the screen and the paper stops being a mystery.