Hi Sally,
First point i would raise here is Why your PM order is kept open even after doing confirmation. The main purpose of this TECO is to say, the maintenance work related to this order is completed, which means you have issued the materials and labour hours are already planned. Still you can do invoice posting as well as labour confirmation.
On the settlement part, you can settle the order during Rel status also. Most of the companies have daily settlement and monthly settlement, they will settle the cost for all orders which are REL and TECO.
If the corresponding month is closed, then system will not allow you post the cost for PER type settlement. In such case you can try by choosing FUL and run the settlement.
Regards
Terence