You can get
to the first item beginning with L by pushing the L key. (You don't need
alpha first on the TI-89.)
Highlighting
and pushing ENTER copies the command to the command line of the HOME
screen.
The bottom of the screen shows the syntax you need for this command. For limit( you enter the expression whose limit you want, the variable, the point the variable approaches (a number or infinity), and optionally a positive number if you want the limit from the right or a negative one if you want the limit from the left. Separate these entries with commas, and supply the close parenthesis at the end.