How can you? It is not possible to feel the positivity of wanting to do something (motivation) when you feel worthless, empty, defeated.
So how to get through those feelings and emerge into a space of motivation? After all, you can't fake motivation - it just becomes a form of self violence.
The way to 'return' to a state of 'motivation' is to discover why one has become 'de-motivated' in life, in the first place. There are likely to be aspects you do not wish to engage with - can you discover why? Can you do so without judgement? Perhaps you will see that there are one or two things triggering fear or reluctance, and this then blooms into full-scale demotivation and reluctance to do whatever it is.
Can we observe our own thoughts and reactions? It is very powerful!
Once there is some understanding of the mechanics and dynamics of what makes one tick - eg what triggers the motivated and demotivated states, it is then possible to do something about it if one wishes. We can go as deep as we like, self knowledge and understanding is EMPOWERMENT. When you feel empowered, you are also motivated to action.
Distractions do not motivate. If one is feeling defeated, and chooses to watch a movie or get drunk to take the mind off, this may work to some extent, but if the underlying causes and triggers of 'feeling defeated' are not understood, the cycle will certainly repeat itself!