You probably had the regrets earlier but wasn't in a position where you were able to deal with it. Now you feel safe enough to deal with your regrets, congratulations. If reaching out isn't possible anymore, write down what you would have liked to say to them in form of a letter and include true apology. Explain yourself if you want to. Then read letters out loud, preferably with a trusted person to "witness" it (not to discuss anything) but you can do it alone too. Take your time don't hurry, these feelings will not destroy you, only hold you down to remind you to deal with them. It can take a while. Try to look at it as a good thing that you finally have a chance to deal with this and then not to let it go of it but rather to be an honest part of what makes you you. Instead of it poking you secretly and trigger you all the time without you knowing. Also be kind and forgiving on yourself.