"Move on" is usually short for "accept it".
Generally if you are not "letting something go" you are re-running it in your head and making changes with your thoughts until you imagine a better scenario.exp "I could've said this" or "why did they do that" ect
How to "move on":
1.Understand carefully that the event you going through was inevitable
-You did not choose to be put in those situation , while the statement being cliche but everyone did a mistake its a vicous cycle
-If you're letting something go then you need to accept what happened and move your thought the hell on.Stop trying to change anything about it or "fix" it or get it back.The thought arises and you dismiss it .In fact , Dwelling on the past itself is generally harmful.
2.COPING MECHANISM
-distract yourself with something you like to do , getting yourself an ice cream , actively involved in your hobby , talk with your favourite person.Rewarding yourself to dismiss the thought are always helpful
-Keep yourself busy , look up to some small thing you want to do.Get ahead of news , reading can distract your mind a little bit.
Thats only from me
I wish that you're able to keep strong and move on to better life