I had a free resume evaluation thing done to my resume and this was what was suggested to me regarding "I did x, resulted in % effect" and I don't know how to c

I had a free resume evaluation thing done to my resume and this was what was suggested to me regarding "I did x, resulted in % effect" and I don't know how to calculate that as a task do-er person / working on a site that doesn't make money yet (but being paid by site owner to develop features). You also mentioned the how to calculate part which may imply having access to the site owner's data (however that may be, ask them) but I think it's hard to calculate those figures/don't know how to. You probably have to wait too to see how your changes have impacted their site, by changing a CTA button color to "blue" and then you say "In 2 weeks, we noticed 150% growth in conversions" or something.