Start by assessing the damage done so you understand how severe the damage is. Now, dig up the plant and trim the roots that are damaged. Once that is done, you need to get a new pot, fill it with new potting soil, and plant your Pilea in it. That’s pretty much it–after that, you just have to care for it in the long term for it to thrive.
Pay attention to the light it gets and also look for signs of improvement like growth and healthy green foliage.