Welcome to the forums!
It shoudn't be overly hard to repair but first you need to scrape off what's loose and see what's left. If only the top portion [bubbles] come off - it's an easy fix. Where it gets complicated is if all/ most of the plaster comes off.
If only the paint and top layer of plaster come off all you need to do is add a coat of joint compound, sand, prime and paint. If the underlying plaster is chalky, you should prime prior to applying j/c.
If most of the plaster comes off and you still have something to attach the the mud to, you can use a setting compound like durabond to fill it in. Durabond/EasySand doesn't sand well so it's best to apply it neatly. I normally use durabond for any plaster repairs, it works well, just isn't as user friendly has ready mix joint compound.
If you are basically left with a hole in the wall [nothing for the mud to stick to] it would be easiest to insert a piece of drywall, smooth the transision with j/c, prime and paint.
Don't forget you are working on someonelse's property. It would be best to get their permission first! Also if they were to determine that you damaged the property by an improper or unsightly repair -
they can hold you finacially responsible 