the CTC is calculated on form 8812
for most taxpayers the CTC is the smaller of 1) $3,000 ($3,600 for children under 6) multiplied by the number of qualifying children less the applicable phase-out amount or 2) regular tax and AMT tax reduced by certain credits but this limitation doesn't apply for taxpayers who had a principal US home for more than 1/2 of 2021.
you say you didn't live in the US for 6 months therefore you should have to repay 9300 less 3187
are you sure it's the CTC AND NOT THE RECOVERY REBATE OR SOME OTHER CREDIT