Can someone tell me what i need to do to join the SAS as a foreigner(im bulgarian)?

There are two parts to answer for this question. 1. The eligibility requirements for the British Army can be found at https://jobs.army.mod.uk/how-to-join/can-i-apply/ . This would be the first step to see if you were able to join. 2. If you are able to join then you would go through basic training, arrive at regiment and look to get recommended by your chain of command, over a series of reports, to attend Special Forces selection. The selection process is understandably very challenging with relatively few being chosen to join each year. If you were unsuccessful on selection you would return to regiment in your previous role.