This is my Marlin firmware for my Ender 3 with a BLtouch added using this mount.
The board I'm using is the BIGTREETECH SKR Mini E3 V1.2 using the BLtouch as the Z endstop.
Some of these settings WILL NOT work for you. I have customized probe offsets, drivers, vref's, lin_adv, etc...
I zeroed the Y axis and noticed the hotend sticks over the edge, so to zero the Y axis I moved it forward until it cleared the binder clips (Y = 15) then moved it until it got to the second set of binder clips, with subtraction you get 210 from clip to clip (give or take)
I then zeroed the X-axis and moved it to the middle of the bed - using the posts underneath the bed to get it as close as possible and measured 115mm from zero which means 230 across.
I used the calibration pattern to figure out what my linear advance value should be, without refining it, I decided to just use 0.56 This could use more tweaking. This will be different for every machine, so set it to zero and use the test patterns on the marlin website to figure this out