this is normal for learning vibro, in most people who are not ambidextrous (aka most people) one hard is typically significantly weaker in mania (and in general) than the other hand. the only real way to get over this is to practice vibro with your left hand more. it is certainly going to be hard but learning vibro in general is hard.
one way to practice this is to just vibrate your left hand's mania fingers on a flat surface like a desk in any time you'd like to build some of the muscles you need
also worth mentioning that you must be familiar with your limits. playing too much vibro can cause hand pain or injuries so avoid that. dont play too much or too fast. if your hands are really hurting than end your session.
finally, you dont really need vibro unless you're interested in pp farming. vibro isnt a pattern, it is a technique that people use as an alternative to jacking when a jack is too fast. instead of improving vibro to edge closer to your vibro goals, first try to improve your jack/jumptrilling abilities. usually you dont need vibro unless there is a pattern that strictly dictates people with or far above your current jacking ability must vibro it. id generally advise to avoid those patterns instead of embracing them.