I wouldn't jump to repot, as Juniper (& other evergreen) bonsai normally don't require it for at least a couple of years, & repotting it at this point could stress it.
What I would do is cut back on the watering. You shouldn't need to water until a finger (or chopstick or similar instrument) poked in shows dryness an inch or so down.
Also, on a most serious note - Juniper bonsai are 100% OUTDOOR bonsai. You can't keep it indoors. It will die. Honestly - do a little online research re: Juniper bonsai. They're seriously outdoor hardy to at least 20 degrees with a little protection. I've had mine for 3-4 years now & it's outside 24/7 year-round except for the few nights when temps dip into the teens or below. Then it comes indoors to just inside the front door where it remains cool, then goes out again the next morning. They really will not survive long as houseplants.
My body is a temple. Unfortunately, it's a fixer-upper.