You need to apply the OnPCSkillUseEvent.diff
Check this links on how to apply a patch
https://rathena.org/board/topic/102828-how-to-apply-diff-file/
https://rathena.org/board/topic/91246-patch-with-git/
But for me, prefer to do it manually. Doing it manually means you need to look for the changes made in the diff file and apply it to your files.
Sample.
Index: src/map/npc.c --> open src/map/npc.c
===================================================================
--- src/map/npc.c (revision 100644)
+++ src/map/npc.c (working copy)
@@ -4350,5 +4350,6 @@ void npc_read_event_script(void)
{"Die Event",script_config.die_event_name},
{"Kill PC Event",script_config.kill_pc_event_name},
{"Kill NPC Event",script_config.kill_mob_event_name}, --> Look for this part and add the new data
+ { "PC Use Skill Event", script_config.useskill_event_name }, --> This is the new added data on npc.c
{"Stat Calc Event",script_config.stat_calc_event_name},
};