Not used the Grbl software. I use an smc4-4-16a16b controller unit for my machine and VCarve for design/gcode. I'm also no expert, but you should be able to move your spindle to where you want the job to start. Move your z so your tool bit is almost touching the PCB. In your software, you should then be able to reset the x,y and z co-ordinates to 0. This will be the start point for your job.

That's how I do things. If you are unsure though, best wait for someone who has experience with the software to make a post.