Yennefer the last wish explanation?

Yennefer talks about removing some magic between Geralt and herself by taming a djinn and telling it to remove the magic. What does she mean ? (never played any other witcher games)

Solution 1:

Spoilers for "the Last Wish" (basically a full recap) below:

The story "The Last Wish" is about Geralt and Dandelion accidentally releasing a djinn. Danelion thinks it's going to grant his wishes, but Geralt thinks it's going to attack them. He tries to banish it using an incantation he heard but doesn't understand. The djinn roars and flies away. Geralt goes to the nearby city where Yennifer is staying, to seek her advice.

In that first meeting, he starts falling for her, while she is simply curious about him as a witcher. Hearing his story about the djinn, she plots to capture it, as it is immensely powerful and could be used to fuel her magic. She knows it will come back for Geralt and Dandelion, so she has them imprisoned to lure it back.

Geralt is talking to the guard and expresses an offhand "wish you would burst", and the guard actually does burst. This allows Geralt to escape, and makes him realize the djinn actually was granting his wishes. He has one left, and goes to stop Yennifer from trying to capture the djinn.

He finds her struggling with it, and we don't know if she has enough power to win or if it will break free and kill her. She tells him to make his third and last wish, which will free the djinn from him and allow her to trap it. He fears that she is too weakened by the struggle and will be killed if he frees the djinn. He comes up with an idea for that last wish that will also save her life, and makes it.

It works. The story does not allow us to hear the actual wish itself, but another character speculates about "tie his fate to hers", and Yennifer hears it and comments about "you've condemned yourself to me". Presumably it was something like love or binding them together. This begins their... let's call it "tumultuous" relationship which continues in the following stories.

In a humorous touch we learn that the "incantation" Geralt attempted initially translates roughly to "get out of here and go f-ck yourself". This was his first wish to the djinn and explains why it was so angry.

Solution 2:

In the story "The Last Wish", by Andrzej Sapkowski (author of The Witcher books), a djinn is released.

At the end of the story, Geralt makes a wish that isn't fully explained in the book, but seems to result in his ongoing relationship with Yennefer.

It seems likely that this is what she is referencing (as in the comment on your question).