Without a remote control; you can't. If you wish to get some details; check the site linked here. Pull up older posts.
Unlock procedure and to override the password lock of many popular brand TVs and other devices are given. Search the site by type in this key phrase "How to unlock television"; in the search box at the top left of the display window, to get gathered related posts.
If you wish to buy its original remote control, contact the authorized service centre, or authorized dealer to your device brand. They can either give you a genuine remote control to your device, or can direct you, from where can you purchase a suitable one.
To select a proper universal remote control, you should know about the number of digits to its set-up codes. There are 3 digit, 4 digit, 5 digit, 2 digit and even single digit codes, to some brand devices. After confirming this, check the sites linked here. Both the sites have set-up code list and set-up procedure to many popular brand remote controls. Check which brand remote control has set-up code/s to your device brand, and buy that one according to availability. Brand name of the remote control isn't a matter, but it should have set-up codes in its code list, to the device brand you have.
Please note: Every new universal remote control will have set-up code list, and set-up procedure along with its pack. Never accept a remote control, that hasn't both of this. For more details about the set-up codes, visit the sites.
Universal remote controls are available at most of the electronic spare part selling shops. Visit some on-line sites too, which deals with electronic spare parts.