The front brake is fine, but the rear brake pulls almost to the handlebar, and needs to be pumped repeatedly to grip.

I'm not the sharpest potato in the sack, but "don't operate a powered vehicle with imperfect brakes" seems pretty basic.

🤔🤔🤔 if you say so...

Is it something you can learn to do yourself?

Eventually, yes, but it takes some specialized tools and equipment, and it's easy to mess up if you don't have the experience.