The typical outgoing bow on the bottom of the print, next to the surface, is called „elephant foot”.
Adjust the first layer
You can use your slicer´s settings to increase the height or extrusion rate for the first layer only. Be careful, because the layer height influences also the adhesion on the printbed. Try out in 5% interval.
If the first layer height is too low or the extrusion rate too high, the plastic smooshes against the printbed and squeezes out of the gap between nozzle and printbed. The result is the typical outgoing bow on the bottom of the print, next to the surface.
Design a chamfer
You can use your construction program to add a chamfer to the edges at the bottom of your part. Be aware, not always the real bottom of your part is placed to the printbed. Adapt the side of your part, you place to the printbed.
To eliminate the elephant foot this chamfer should be quite small.
This is solution is only for users who know how to construct parts and who to create .stl files.
To level your printbed and to set the height of your nozzle properly, please follow the instruction of your 3D printer.
To set up the proper nozzle height or more accurately, set the correct zero position for the Z-axis helps reduce warping, getting rid of an elephant foot, but also helps to extrude the right amount at the first layer. Most 3D printers do not have a way of sensing when the nozzle touches your print surface, they just rely on an endstop or a separate sensor to probe the bed. For both cases, you usually need to manually set the zero position. The exact procedure differs from printer to printer, but the general idea is usually the same:
Make sure the nozzle is clean and ideally, heated up so that any boogers will get wiped away by the paper.
Use a thin piece of paper for stiffer beds (about 90g per m2 or 0.1mm thickness) and a thicker paper for springy beds (about 300g per m2 or 0.25mm thickness, e.g. a business card).
Adjust the endstop or sensor offset until you can feel a slight resistance from sliding the card around when the printer is at the zero position for the Z-axis. Most printers have a semi-automatic mode, by which the print head travels to several defined spots on the print surface and you have to set up the nozzle height manually. If not, start in the centre of the bed for a first rough adjustment, make your way around the bed and repeat for each adjustment point. Move the print head as close as possible to the adjusters and tweak them until you get an even resistance with the calibration cards at each of them.