What is the correct Marlin firmware setting for Tevo Tarantula with MKS Base V1.2 board I am trying to correct the x&amp;y offsets in the Tevo Tarantula that I got from a friend in order that my printer is not printing over the end.
What I got so far is that I need to measure and then enter the offsets into my configuration.h file, build the firmware and flash it to the board.
Because I do not have and can not find the original firmware I found the repository from Jim Brown for the Tarantula.
Looking into the top section of the config file provided by the repo, the board configured is
#define MOTHERBOARD BOARD_MKS_GEN_13        // Original controller board with built in stepper drivers. Works with MKS BASE 1.3, 1.4

However since the board in my Tarantula has 1.2 on it I checked the boards.h file for MKS but could not find the v1.2 :
#define BOARD_MKS_BASE          40    // MKS BASE v1.0
#define BOARD_MKS_BASE_15       405   // MKS v1.5 with Allegro A4982 stepper drivers
#define BOARD_MKS_BASE_HEROIC   41    // MKS BASE 1.0 with Heroic HR4982 stepper drivers
#define BOARD_MKS_GEN_13        47    // MKS GEN v1.3 or 1.4
#define BOARD_MKS_GEN_L         53    // MKS GEN L
#define BOARD_MKS_GEN_L_V2      54    // MKS GEN L V2
#define BOARD_ZRIB_V20          504   // zrib V2.0 control b

Any idea, what board configuration would be compatible for 1.2? Or is there any other way to correct the x&amp;y offsets other then compiling them into the firmware?
The MKS Base v1.2 is basically an Arduino MEGA2560 and a RAMPS1.4 on a single board.
You can use the RAMPS pin designation.
Note that the endstop to origin distances is explained in question How to center my prints on the build platform? (Re-calibrate homing offset).
In Jims Marlin fork you can find this at:
#define X_MIN_POS 0 - XTRA_BED_LEFT

and
#define Y_MIN_POS 0 - XTRA_BED_BACK

Unfortunately, XTRA_BED_LEFT and XTRA_BED_BACK are defined as zero; this implies that the endstops define the origin (not likely) or it is left as an excercise for you to find out. This answer explains how you figure that out.