I have an inexpensive RCA universal remote we use with an old Magnavox TV.  It stopped working for some reason so I needed to try reprogramming it.  Searching on the Internet I found this advice:

1. Remove the battery cover on the back of the remote and look for the model number ("RCR6124609P" for instance)
2. Consult list of TV codes for your model via: search online

Sure enough, on the back of the battery cover I found the code RCR311B. Searching online I found these instructions which worked for the remote:

1. Manually turn on the TV
2. Press and hold the TV button The illuminated ON•OFF key turns on and remains on.
3. While holding the component key down, press and hold the ON•OFF key. The illuminated ON•OFF key turns off.
4. After holding down both keys for three seconds, the illuminated ON•OFF key turns back on.
5. Release both keys. The illuminated ON•OFF key remains on. TIP:
Throughout the programming of each key, be sure to keep the remote
pointed at the IR sensor of the component you are currently programming
the remote to control.
6. Press and release the ON•OFF key
repeatedly until your component turns off. Each time you press the
ON•OFF key, the illuminated ON•OFF key blinks, and the next
code
in the list is sent. This process continues until all of the codes in
the Code Lists have been searched. If your component turns off, you
have found the correct code.
TIP: Because there are so many codes, you may have to press the ON•OFF key many times-possibly up to 200 times.
7. Once you have found the correct code, you must save the new code by
pressing and releasing the STOP key. The illuminated ON•OFF key turns
off. You must press the STOP key to save the code or the correct code
will not be stored!
8. To confirm that the component key is
programmed with the correct code for maximum functionality, test the
component. Attempt to control a variety of the component's functions
with the remote. If some of the features of your components do not
work, try programming the remote with a different code in the list
until you find the code that allows the remote to control the majority
of your component's functions. Different codes can provide different
levels of functionality.