There has been limited damage to some of the leaves, but otherwise, your Ficus elastica looks healthy. The leaf damage was doubtless caused by the poor care it received at the florist. It was probably neglected and the soil allowed to get so dry that some of the leaves developed the dry patches. The brown patches will never re-green so you can either trim off those patches or the entire leaf - just to make it look nicer.
It appears to be in the right sized pot and root rot is not a likely problem. Keep it in that pot and in the east window that should be completely uncovered throughout the daylight hours. Water it thoroughly as soon as the top half-inch of soil feels dry. Although the damaged leaves will not recover, I think you will be rewarded with healthy new growth coming in at the tops of the stems. Leave the roots alone and don't try to do too much because it is in pretty good shape overall.
