If you have no reference at all about the inserted positions of a detector, the safest way is, to move it in by hand first. Retract the VLM and then push the buttons for XDET, YDET and ZDET so that the detector will be roughly centered in the inserted specimen stage. Don't move it too far upstream at this early time though. It is safer to leave a few mm space between the detector and the sample stage for now. Then go to Alignment Edit Alignment Record Advanced and record the pertaining detector to be aligned. You may test this alignment, by removing the detector and then inserting it again (Alignment Edit Alignment Detector: Insert XY). Be prepared though to push the STOP ALL button on the MM3000, if something doesn't fit right.