I've learned it entirely by myself, as back in the days there were no tutorials and it was one of the main philosophies of the engineering course: "learning to learn"; and many of my friends in the Mechanical Engineering course did it as well. I was given SolidWorks 98 when it first came out after attending a workshop where they gave away a CD and free license. The software was quite buggy but had a huge potential and it was a novelty at the time, as no proper 3D CAD existed yet. Before that, I was an AutoCAD (MS-DOS) user, also learned it by myself.
SolidWorks 2000 was a lot better than 98 and much more stable, I spent a little over 10 years using SolidWorks daily before I changed jobs and had to learn Autodesk Inventor by myself. I never bothered to get certified in any of the dozens of engineering softwares I learned, as certification is generally aimed at young designers and professionals from other fields that don't inspire confidence, not engineers, in order for them to secure a new job that would normally require a minimum of 2 years experience using the software to ensure they hit the ground running, so the certification would provide confidence to the interviewer that the designer or non-engineer can perform as well as anyone else despite not having the required experience or knowledge.
For engineers, usually the work environment does not rely solely on using the software, or the company already regularly pays for the training, so not being certified should not be a big deal. If you're eager to learn the software by yourself, companies would have no problem hiring, as they're hiring much more for the other knowledge you've got. Also, from your post, you are already working for a company that uses the software, so again I see no point in getting certified. Just grab a few random objects you've got around and a caliper, measure them and try to create 3D models, there's also plenty of tutorials online to help you become more efficient. That was the method I used the first time, and the method I used when I was teaching SolidWorks in the Mechanical Engineering course (I would first give a ~5 minutes introduction to explain the interface and the working logic for sketch, part, assembly and drawings, and then each student would be given a random object and a caliper, as simple as that).
