DURING MEDICAL EXAMINATION FOR US IMMGRANT VISA, IF THE CHILD (AGE 5 YEARS) HAS TST VALUE IS =>10 MM OR IGRA POSTIVE, WHAT WILL BE THE NEXT STEP?

Children, whose tst or igra shows positive and previously had no history of TB, the next step will be the Chest X-ray PA for children aged 10 years and less than 15 and Chest X-ray AP lateral view will be required if the children is 2 to 10 years followed by further steps in case of abnormal Chest X-ray. That's the next step which is mentioned in instruction.

Chest X-ray to be run on that child

I'm not sure how helpful this will be, but the Department of State gives guidance here: https://travel.state.gov/content/visas/en/immigrate/immigrant-process/interview/prepare/medical-exam-faqs.html

They say, "Applicants with a previous positive skin test for tuberculosis should provide a certificate from the attending doctor (giving the circumstances of the positive test result, and indicating any treatment prescribed, and its duration) to the panel physician. If the applicant has ever been diagnosed with tuberculosis, the applicant must present a written certification, signed by the attending doctor, proving that the applicant was adequately treated. The certificate must include dates and types of medications taken. Applicants who ever had an abnormal chest X-ray should borrow the last X-ray films taken and bring them to the panel physician. The actual films, not the typed reports, may be required to compare with the X-rays that will be taken at the medical examination."