It was so easy to make friends during my undergrad because I lived in the dorms. But I lost half of them due to a messy situation with my ex girlfriend, and the other half doesn't live in town anymore.
Now I'm 22, working on my Master's, and I feel like I have no one.
Talk to people in your field, the PhD candidates, other MS students, hell even the undergrads
Pick up and engage in social hobbies. If you're sporty regularly showing up at pickup games is a good way to start, for more nerd inclined joining a game, book, or anime club. The idea is find a social setting for something you love doing so it's less pressure for everyone involved
Go out to the social centers- bars, parks, malls- if you find a place you like you can get to know the regulars
Join a singles activity group- these aren't just for dating
One last tip, try to organize an online game night with your friends who moved away, discord has a couple built in and I highly recommend boardgamearena.com