I don't know the answer, as I struggle at times with the same questions. I get discouraged easily, I get overwhelmed by not knowing where to start with the plethora of problems that populate my life.. What does help with me is just giving myself the space to experience whatever it is that a depressive episode is there to teach me though. Which is to say, accepting that it's a part of my life and as such is serving some organic purpose however mysterious, and that it's much better for me to respect the existence of my depression however much a struggle it might be than it is for me to demonize it. That's what works better for me anyway. Acceptance doesn't have to represent complacency or submission.

Something else to consider: there has been research pointing to positive affirmations having the potential to be counter-productive, if they feel out of reach or inauthentic to a person; maybe start with something smaller? I couldn't guess at what might be more authentic for you, but if it was me (and I am in the process of improving my physical health with regard to weight and better nutrition, however slowly).. I might go for something along the lines of "it's within my power to ignore this hunger pang, just for the rest of this day". Similar to how those in AA talk about addressing their sobriety just one day at a time.

Good luck