You should try diffrent streching exercises which remove tightness..u also do a exercise on physio ball which verry effective on your case...for all this u should consult physiotherapist near u...

when we sit, the spine becomes stuck in flexion, obstructing the obliques and reducing mobility. To help break up the scar tissue, you can start with “warming up” the tissue in the area first. You can use a massage cream or lotion than start mobilising up n down and side to side . Don’t go directly over scar tissue You need to do few exercises to reduce the tightness of muscle

U need to mobilise scar manually and stretch scar .. ultrasound is old school of physiotherapy u can try that

Rather than opting for ultrasound you should better opt fir stretching exercises and soft tissue manipulation at that area along with application of an ice pack for 3 minutes after exercises.

You should do massage therapy. Do not apply ultrasound directly.