How is the choice of the right branch implemented in selfish mining?

Question

bitcoin

There are two small questions.
1) From a practical point of view, how does the switch from a short branch to a long branch occur (for example, with selfish mining)?
2) Are there any solutions to avoid double spending in selfish mining? So far, I just haven’t found any information on how double spending is avoided, and this, as far as I understand, is one of the main problems of selfish mining