It is preferred to get the distance correct by hardware changes (leveling screws). But it is possible to do it with software. You can not only change the Z offset in the slicer or in the configuration of Marlin, but also with G-code commands.
The "paper drag" method is perfect for determining the correct Z level. Once you leveled with the paper, you do not need to create an offset to account for the paper thickness, however, there are purists that do that. So basically, what we call Z=0 is in fact Z="paper thickness", unless you are a purist. But a slightly larger gap makes printing much easier. Too small heights cause e.g. rippling effects or too much pressure build-up in the nozzle. In order to change your offset after leveling, you could try one of the following methods. This is sometimes a useful method for creating a little extra offset for printing PETG, but personally I do not do that.
In Ultimaker Cura:
Open the plugin manager ("Toolbox"->"Browse packages...") and install "Z Offset Setting", a new parameter will be available in the "Build Plate Adhesion" settings menu called "Z Offset". (See also this older, not up-to-date answer)
In Marlin configuration file, modify the MANUAL_Z_HOME_POS constant:
//#define MANUAL_Z_HOME_POS 0
By adding the following lines to your start G-code (see e.g. this answer) using the
G92 G-code command:
G0 Z0.2 ; Move the head to 0.2 mm (so now 0.3 on your machine)
G92 Z0 ; Call this Z = 0
or when you are able to connect to the printer over USB using a printer terminal (e.g. Pronterface, Repetier or OctoPrint) using the
M206 G-code command:
Use M206 to apply a persistent offset to the native home position and coordinate space. This effectively shifts the coordinate space in the negative direction.
M206 Z-0.2 ; Will raise the Z height by 0.2 mm
M500 ; Stores the offset in memory
Alternatively, when you cannot connect through a terminal, putting the last 2 lines in a text file and saving that as a
.gcode file on an SD card and "printing" the file will also store the new offset (if
M500 is enabled in the configuration file:
#define EEPROM_SETTINGS // Enable for M500 and M501 commands)