A / Replacements Points
Replacement Points (see in Illustration 13.1 below) are used to repair units that have been damaged previously, either in battle or via events or card play. Damaged units that have lost at least half of their hit points are showing a white stripe across their counter.
When you receive a Replacement Point (RP) you just need to select which unit will receive it among the eligible ones (a unit is eligible if it has suffered at least 1 point of damage). When you are unhappy with the assignment, click again on the unit and the RP will be removed and returned to your stock. Unused RP will be lost (you will receive a warning about it).