there are plenty of threads about this but....
the first stage is just like a regular old boss, just shoot/slice/etc. it untill it dies.
the second stage gets a little trickier:
olga has the two little things that float around his feet and make his attacks stronger. you can't kill them, but you can injure them and KO them temporarily. (highly suggested by 9 out of 10 dentists

)
olga will also turn orange every once an a while, and one of you'll turn into Flowen (its just the looks, you don't get a power boost or anything). during this time if you attack olga the person who looks like Flowen will get recoil (like with falz's soul steal) UNLESS you are using a weapon with the correct %'s or the right tech.
when olga gets orange he will become weak to one of: native, beast, machine, or dark AND one of: fire, ice, lightning, or light. any other attack will do recoil (as stated above). if olga becomes weak to native and ice you can use any weapon with a native% (it can have 15/0/0/0, or 25/0/50/30, it just has to have that one type) or you can use a barta tech.
there is no way to tell what weapon/tech you need without testing it out EACH TIME he turns orange. forces will need grants even in normal mode. it is also good if you bring weapons (guns moreso than swords) that have %'s in 3 areas.
Too legit to quit.