Ditched my retainer and my teeth have moved. What can I do to bring them back ?

I had a retainer for 2 years to pull in my top teeth as I had a huge over bite. Following this I had braces for another 2 years. After my treatment I was given a clear set of retainers to wear at night. I wore the clear retainers for about 1 year. I had my braces off at 15 & I'm now 22. I feel as though my 4 front teeth on top have moved & I don't know what to do about it. I still have my retainer. How do I fix this problem ?

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