A. If you feel a real possibility: ‘If I ~’, ‘I’ll ~ ‘can be used. When you imagine a situation, you use ‘if + past’ (if I knew/ if you were/ if we didn’t etc.). But meaning is present, not past.
A1. use the past in the same way after ‘wish’ (I wish I knew/ I wish you were etc.). We use ‘wish’ to say that we regret something, that something is not as we would like it to be.
A2. After ‘if’ and ‘wish’, you can use were instead of was (if I were ~/ I wish it were etc.). I was/ it was are also possible
A3. We do not normally use ‘would’ in the ‘if-part’ of the sentence or after ‘wish’.
A4. ‘could’ sometimes means ‘would be able to’ and sometimes ‘was/ were able to’.