Newbie coordinates question, positioning work relative to machine

I'm not sure this is the right sub forum, but here goes! How do I position an NC file toolpath relative to the machine coorfinate datum? I'm going round in circles reading the G54 et al documentation and I'm not finding a really simple guide to my most basic problem. After loading the NC file, the part datum coincides with the machine datum, but the part hangs out of the side. If I can shove it over it will fit.

Screenshot and picture?

Haven't figured out how to do a screenshot in Linux, will give that a try

So now I know how to screenshot!

Move the machine to the start of the workpiece, click on "touch off", set 0, press enter.
Repeat for all axis.

Thanks. I know it sounds dumb because I guessed it was what the touch off button was for, but it just hadn't clicked how to drive it.