If, after 14 days of being notified of your positive decision, you have not received your eVisa sign in details, you need to check with your legal representative or responsible adult as they may have received the information on your behalf. 

If neither you, your legal representative or your responsible adult have received any information about your UKVI account within 14 days of a positive decision on your asylum claim, you can ask for help here: https://ukimmigration-support-webchat.homeoffice.gov.uk/evisa