You use
https://p2t5r.itch.io/ego-erp-archiver then open the teams' erp files 2018_asset_groups\f1_2018_vehicle_package\teams\ export the vtf files and change the exported xml files with an editor like Notepad++.
Change the chassis mass, try to play around and see what you'll get. Remember: A car does not make the pace, the driver does. So even if you make all cars equal, bad drivers will drive slow overall.
After you have done and saved your changes, reimport the files with the EEA again back to the erp files.
Or you could have used the search function, since this is something that is from since 2017 til 2020 all the same.