I've gotten in the habit of reflecting on gratitude whenever I'm sad or in a bad mood. It really changes things around for me personally. You don't have to force yourself, just thinking about gratitude in general is useful.
Reviewing the day with gratitude is a core tenet of Ignatian mindfulness. I do an expanded version of the talk with my wife, with God, using a version of the instructions shown at https://www.ignatianspirituality.com/ignatian-prayer/the-exa...
So I hope that you will do the same for the rest of your lives. When things are going sweetly and peacefully, please pause a moment, and then say out loud, "If this isn't nice, what is?”
-- Kurt Vonnegut