You can’t “Increase the Texel Density” of a Mesh. That’s not a thing. What you can do modify it’s UV coordinates.
You see, UV coordinates define in a 0 to 1 space where on a texture will a triangle covers in the simplest of terms. UV coordinates are independent of Texture density. whether your texture is 64 by 64 or 8K by 8k, 0 in the horizontal axis means all the way to the left, 1 means all the way to right, and 0.5 means in the middle.
Either the resolution of your textures is to low or your mesh is improperly unwrapped.