It's just better to get used to a baseline level of misery than relying on happiness to get yourself out of a funk.
That said, turn the fucking devices off, get a big fucking cup of herbal tea, and look at the natures for 30 minutes. You are not allowed to press the buttons on the misery-skinner-box until tea is gone and timer is up.
Take a nice shower,get to yoga class even on the days I don't feel like it, treating myself to a nice book or random thing I want, talking to my therapist and letting it all out.
Lists, strong emotive music, niche interest rabbit holes (preferably new) and awful people (It's always Sunny)... I also clean if I'm able, short bursts usually.
Let whatever is causing your negative emotions to overwhelm and release. It’s incredibly cathartic and you’ll feel much better if you just give in and let it happen. The reason doesn’t have to be anything super important, or could be something super important; regardless crying should be embraced as an act of self care.
I do something creative that lets a little secret part of me out. Those things I feel guilty enjoying (because I feel like I'm not good enough at them to do it, like singing or painting). It's like a little special indulgence that also reminds me that I'm pretty cool.