If all of your metabolites used the same dilution series, but all of their series concentrations need to be multiplied by a different number because the starting concentration was different, then you can use the Document Grid to set the "Concentration Multiplier" value for each molecule. The Concentration Multiplier of the molecule gets multiplied by the Analyte Concentration that has been specified on the replicate.

If your metabolites each had a different dilution series, and you need to specify a different concentration for each metabolite and replicate then you can set the "Explicit Analyte Concentration" for each Molecule and Replicate.

If you need to learn more about the Document Grid you should look at the Custom Reports tutorial:
https://skyline.ms/wiki/home/software/Skyline/page.view?name=tutorial_custom_reports
-- Nick