You can use Bragg's Law.

For detail, you can read following link and attachment.

https://www.researchgate.net/post/How_can_I_calculate_lattice_parameters_a_b_c_from_XRD

Lattice parameter of the metal oxide can be measured by the Bragg's Law-2dsin θ = nλ

d=Interplanar spacing of the crystal, θ=Angle of incidence,

λ=Wavelength of the incident x-ray, and n=an integer.

You can calculate lattice parameters from XRD data by using different methods:

1) By manually indexing the peaks using linear intersect method

2) By Rietveld refinement of the XRD pattern, etc.