Websites like Remont-Aud.net or 4PDA often host split RAR firmware files for TCL models. You will need to search for "TCL LED43S4900 firmware" or "MS6486" (the common mainboard chassis for this model) to find all parts (Part 1, Part 2, Part 3, etc.) in the same thread.
These archives are typically split. You must download all parts (e.g., part01.rar, part02.rar, part03.rar) and place them in the same folder, then extract only the first part using tools like WinRAR or 7-Zip. Download TCL LED43S4900 Firmware part03 rar
Before downloading, confirm the mainboard number in your TV (e.g., 40-MS6486-MAA2HG). Firmware for the 43S4900 is often listed under the mainboard number rather than the TV model number. Websites like Remont-Aud