This May Help
If you have a Uniden Bearcat 340CRS (you did mention its a 340) you press "Hold" to go to whatever channel you want to enter a frequency, then "E"/PGM, then enter your frequency including the decimal (might have to hit zeroes at the end to make sure its all 6 digits, for example, 155.490 not 155.49), then hit "E/PGM" again. To program the next channel up, simply pressthe up arrow then enter new frequency.