We usually use the construction I wish+past simple to express the wishes about the present or future.
We can use 'wish' to talk about something that we would like to be different in the present or the future. It's used for things which are impossible or very unlikely.
- I wish I had a big house (I don't have a big house, but it's a nice idea!).
- I wish we didn't need to work today (we do need to work today, unfortunately).
- I wish you lived close by (you don't live close by).
- I wish John wasn't busy tomorrow* (he is busy, unfortunately).
We also use 'wish' with 'could' to talk about things in the present or future that we would like to be different. In this situation, 'could' is the past simple of 'can'.
Of course, we use 'can' to talk about ability - if we know how to do something or not. For example, 'I can speak Spanish' or 'I can't drive'. We also use 'can' to talk about possibility - if things are possible or not possible. For example, 'we can't come to the party tonight' or 'John can help you clean up'. We use 'could' with 'wish' to talk about ability and to talk about possibility.
- I wish that I could speak Spanish (but, unfortunately, I can't speak Spanish).
- I wish that I could drive (I can't drive).
- I wish that we could go to the party tonight (unfortunately, we're busy so we can't go).
- I wish that John could help you clean up (John is at work, so he can't help).