Question

in which part of the letter does travis ask for help and reinforcements?
i have sustained a continual bombardment & cannonade for 24 hours, and have not lost a man
i am besiged by a thousand or more of the mexicans under santa anna
i shall never surrender or retreat. victory or death!
i call on you in the name of liberty, of patriotism....to come to our aid, with all dispatch

Explanation:

The phrase "to come to our aid" clearly indicates a request for help and reinforcements.

Answer:

I call on you in the name of Liberty, of patriotism.....to come to our aid, with all dispatch