I have been going to PT and the therapist said I was starting to develop some scar tissue that is restricting my ROM it was 110 but has decreased to 100.
Your PT has told you wrong, on several counts.
The type of scar tissue she is talking about is more properly called adhesions, and they don't form this early in
recovery.
A drop of flexion from 110 to 100 is insignificant. It can even be because of inaccurate measuring. You have to place the measuring device in exactly the same place every single time, and you need to be in exactly the same position every time.
It is most likely caused by a slight increase in swelling, that could have happened because of a variety of things, including increased activity, less time resting and elevating. If you measured flexion at the start of the day, at mid-day and in the evening, you would be likely to get three different readings, with the lowest flexion being in the evening.
Massaging won't prevent, or breakup, scar tissue. If it feels good, do it. If you don't feel any benefit from it, don't bother.
Your new knee is only just over a month old, so you have plenty of time to increase its ROM. You're already at 100-120 degrees and that is great for so early in recovery.
There's no need to rush to get ROM (Range of Motion) because it can continue to improve for a year, or even much longer, after a knee replacement. There isn't any deadline you have to meet:
Myth busting: the "window of opportunity" in TKR