The second way to lock the target. You can identify it only on MAV screen. To lock the target with RDR:
enter RDR page (on the right MFD, for example) and lock the target with RDR;
select MAV page as SOI. After that, mavericks seeker will lock the target and you will see the connected cross. You can press the FOV button on MAV page to see the target closer;
Additional way to lock the target. The main purpose to use it - fast switch between nearly placed targets for multiple launches
on MAV page, selected as SOI, press and hold TDC Depress, than move seeker using TDC Up/Down/Left/Right. Target will be locked after releasing TDC Depress.