There are two things happening here.
Firstly, that little 'bubble' is really a part of the plastic window and nothing to worry about.
Secondly, your fluid level looks to be too high, but that depends on how the bike is sitting. If you sit on the bike and hold it upright and with the bars pointed forward, there should be some empty air space in the top of the window. An overfull reservoir can mean your brake pads won't rest away from the rotor and will drag, causing heat and wear.
You can check this for yourself, and if you are confident you can remove some fluid. Hold the bike upright or get somebody else to do that for you. Position the bike so the reservoir lid is level.
Clean the top of the reservoir thoroughly and fold an old clean towel around it to protect from any spill. Remove the screws. Lift the top off, then lift out the rubber inner cover. Dip some clean and dry fabric into the fluid to lower the level, or use a syringe or similar, until you see some clear air in the top of the window. Replace the rubber cover and the top. Screw it up and you're done.