Use the universal dilution relation: Make sure units are same on both sides.

Cinitial x Vinitial = Cfinal x Vfinal

For example, for buffer Cinitial = 2 M, Vfinal = 500 mL, Cfinal = 0.050 M, solve for initial volume and dilute as desired. One should make up the volume after adding all the components.

Use the universal dilution relation: Make sure units are same on both sides.

Cinitial x Vinitial = Cfinal x Vfinal

For example, for buffer Cinitial = 2 M, Vfinal = 500 mL, Cfinal = 0.050 M, solve for initial volume and dilute as desired. One should make up the volume after adding all the components.

If I understand your question correctly use CV to calculate the NaCl and Buffer content you need.

Then find out the total volume of both and reduced by 500 mal which is the volume of Glycerol.

I believe you wanna prepare the solution in 30% Glycerol

Just do as M. Farooq Wahab suggests: Cinitial x Vinitial = Cfinal x Vfinal. The universal mass balance as you learned in high-school.

Please note 1 M = 1000 mM while doing as per M. Farooq Wahab calculation