I was about to give someone a warning point when i realised... i dunno how.

I checked FAQ's but i couldn't find anything.

Its either ban or delete and send a PM saying dun do it again.

Is there a way to give them a sort of warning.

You can probably send them a PM, saying you have got your first warning.
Also, add a warning level field in their profile as is on this forumotion forum & change it accordingly.
You can see here the procedure how to add the warning level field.
https://help.forumotion.com/other-problems-f46/how-can-i-have-warning-level-on-my-forum-t33390.htm

Hope all this helps.