Do you know if the machine has Grbl 0.9 or 1.1 on it? Was the previous owner running Carbide Motion 3? Best way to check this is to install the current version — if it kicks up an error message that it can’t connect to versions of Grbl prior to 1.1 (or something similar) then your machine most likely has Grbl 0.9 — let us know at support@carbide3d.com
If you intend to use the machine with other software and just want the settings see: