Dear Soumen Pradhan

First you need to know the crystallization system of your sample. Cubic, monoclinic, orthorhombic, or etc.

You can perform rietveld refinement to obtain the lattice parameters, which is a very reliable way to do it.

However, knowing the crystalline system you can obtain the lattice constants with a more manual calculation, employing the formula that correlates d spacing and lattice parameters for your particular system. You can find an image attached showing the equations for each particular system.

Where d is your d spacing regarding the hkl plane that you are using. The more complex the system, more planes will need to be used. So you will have a mathematical system with 2 variable and 2 equations, and so on.

Hope it helped.