What do these sentences mean to you?

1.If you knew you should have told me.
2.If you knew why didn’t you tell me?

But as the “if conditional” rule says,

If + Past tense of verb+rest of the sentence in future tense.
e.g.
3.If he came We would got o party—But the his of coming is very less or not.
4.If he comes we will go to party—(Here the waiting person is guranteed about him i.e. he will definitely come)

But how would you write the sentence using If which will indicate the past happened activity.I mean,
The above sentences No 1 & 2. The user already knew the things but he didi’t tell those.but if you compare it with sentences 3 & 4.

Can you tell me the correct sentence using “If”. As this sentence does not include in “If conditionals” .