1) Undesignate - pressing undesignate you cicle thru targets, to undesignate it all you have to go back to RWS and press SIL and turn it on again.
2) Because in TWS it is relative to the amount of BARs your radar is scanning.
3) it is the Bearing and Range. Top Left where your TDC is pointing to, botton center relative to the nose of your aircraft.
4) Steering Dot. The Steering Dot in conjunction with the NIRD/ASE circle indicates lead angle steering to the locked target. The pilot should fly to place the Steering Dot inside the NIRD/ASE circle to satisfy lead angle computations. The Steering Dot will flash when within 15 degrees of the RADAR’s azimuth limit and when within 5 degrees of the RADAR’s elevation limit. (page 129 of EA hornet Manual)