What can you do if a subordinate refuses to conduct corrective training for missing pt?

Annotate failure to complete corrective training on their counseling. Refer to CoC for UCMJ action, and drop the hammer on them. Unless you're asking or telling them to do something illegal, unethical or immoral as part of the corrective training they can't refuse to comply with your lawful order.

Failure to Repair (Not at Appointed Place of Duty) and Failure to Obey a Lawful Order/Regulation/Policy both Article 92.
Conduct prejudicial to “Good Order and Military Discipline.” is an Article 134 a much more serious charge and can lead to a recommendation for a General Courts-Marshall is if was done in front of other enlisted.
I only recommended one Art 134 in my career and it was for a soldier that "thought" we were going to war in Europe in the 1980s when several MIGs went after a Cobra gunship on the Crezh Border. He climbed out of his Scout M113 at a stop and started walking towards the unit's rear. The Scout SGT tried to talk him back but he refused. The SGT radioed me and I radioed the 1SG. The 1SG picked him and arrested him under the commander's order. He got a Special Courts-Marshall (lowest the Sqdn Commander was willing to go. Reduction to E1, Six Months in Mannheim Lockup and a DD was the result.
I would have thought that the morale would have been on a downturn after the conviction but the Scouts in my Cavalry Platoon were pleased. The consensus was they felt he abandoned them (true) and would have rather seen him get more time .

Would you want to be in the foxhole with a soldier who did not follow orders.UCMJ