You need to supply a little more info on what you want to do. Looking into my crystal ball, I assume that you have the enzyme and a substrate that produces a colour change when hydrolysed.

Then you need to convert the colour change, that is, the change of absorbance, into a change of concentration. This is done by Lambert-Beer's law, using the molar extinction coefficient ελ of the substrate (or product) at the wavelength λ. If that hasn't been published, you need to determine it yourself, I assume that's what you mean by standard curve. Ideally, the absorbance plotted against the concentration is a straight line, the slope is ελ.

If you do determine the substrate or product concentration for several time points, the slope of the resulting straight line is the reaction velocity, v = dS/dt expressed in mol/s = katal. If you determine the velocity at several enzyme concentrations E, you get another line with slope A = dv/dE, the enzymatic activity, for example in kat/mg. Using the molecular mass of your enzyme, you can express that also as turnover number, the number of molecules of substrate hydrolysed per second by one molecule of enzyme.

Please look at the following below links which may help you in your analysis:

https://openwetware.org/wiki/Beta-Galactosidase_Assay_(A_better_Miller)

https://www.gbiosciences.com/Galactosidase-Assays

https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/beta-galactosidase

https://www.aatbio.com/products/amplite-colorimetric-beta-galactosidase-assay-kit?gclid=EAIaIQobChMIzrehy9Hh5AIVSMDeCh1RmQEAEAAYAiAAEgJ8k_D_BwE

https://www.abcam.com/products?sortOptions=Relevance&selected.classification=Cellular+and+biochemical+assays&keywords=Beta+Galactosidase+Assay+Kit&gclid=EAIaIQobChMIzrehy9Hh5AIVSMDeCh1RmQEAEAAYASAAEgK0j_D_BwE

Thanks

The following articles can used to measure Beta-galactosidase by spectrophotometric and Chemiluminometric methods, respectively.

Article Characterization of β-galactosidase from Saccharomyces fragilis

https://aem.asm.org/content/aem/61/12/4505.full.pdf