Truss rods are typically installed during the construction of the guitar neck and require specific modifications to the neck's design and construction to accommodate them. Retrofitting a truss rod into an existing neck that was not designed for it can be challenging and may not be feasible.
If you're experiencing issues with the neck relief or action of your guitar, it's best to consult with a qualified luthier or guitar technician to assess the problem and determine the appropriate solution. They can provide professional advice and perform any necessary adjustments or repairs to ensure the proper functioning of your guitar.