There are many synonyms that can be used instead of "let it go" in various contexts. Some of the alternatives for "let it go" are release, relinquish, abandon, surrender, and forgive.
To release means to set free or liberate oneself from something that has been holding them back. Relinquish denotes giving up control or ownership of something. Abandon refers to leaving or giving up something entirely, while surrender suggests handing over control or yielding to a superior power.
Finally, forgiving is letting go of anger or resentment towards someone who has wronged you. All these synonyms have their own connotations and shades of meaning but can be used in place of "let it go" depending on the context.