How can you bring back old feelings?

Say from an ex or someone you were romantically involved with, if it's been a while since the breakup and they may or may not no longer have feelings for you, how can you bring back those old feelings? Is there a way to salvage them?

I'm looking for helpful answers, not "Just move on" answers, please.

How would you win back your ex to bring up old feelings so they want you back?
How can you bring back old feelings?
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