The navigation tower was a structure located outside Exegol's Sith Citadel during the battle there in 35 ABY between the Resistance and the Sith Eternal.
The navigation tower sent a navigational beacon that helped the Xyston-class Star Destroyers of the Final Order fleet to leave Exegol, since they did not have their own navigation device, so they completely depended on the signal that received from this tower.
Before the Battle of Exegol, the Resistance learned that the Sith Eternal's fleet, the Final Order, required the signal from the navigation tower to leave the planet, so they devised a battle strategy to eliminate the tower. When the Resistance reached Exegol, its forces would attempt to destroy it to prevent the tower from sending the navigation signal so that the Xyston-class Star Destroyers would not be able to leave the planet. To do this, a ground team led by General Finn would be in charge of attacking the navigation tower, while an air team led by General Poe Dameron had to defend them.
Ground forces traveled to Exegol in the transport hauler, but after their arrival, a First Order officer realized that the Resistance wanted to attack the navigation tower, so Allegiant General Enric Pryde changed the navigation signal of the tower to his command ship, the Resurgent-class Star Destroyer Steadfast, forcing the Resistance ground team to turn to Pryde's ship.