A number of ways. The first things you need to assess is why you dont have the desire in the first place? Is it because you can't focus? Look up tips on focus and self-discipline. Is it because you are not interested in the topic? Find interesting case studies and books to read alongside, once you start the snowball you tend to find your interest picksup. Try also working with other people for new and different insights as well as companionship, solidarity and motivation. If possible, change the material of your learning to something which interests you more. Find new ways of learning, there are so many ways of learning and reorganising information in exciting ways – look them up. Mix things up to keep up interest. Find interesting places to study or find that one perfect spot. Set yourself up before learning. Commit to the process, sit down with everythig you need including healthy snacks and coffee if needed. Set a timer for how long for (90 mins is a good time), set an intention and commit. Again once you get started over time, the desire to keep going and start more increases. And look up how to protect and enhance your brain, brain fog and depression are common causes of lack of motivation. Jim Kwik is great for all things brain related and always see your doctor if you think you may be consistently feeling down or depressed.
i say, whatever you are striking for in life, find a way to connect to it. whatever job you want to have or just general learning you want to improve, contact the job place or start courses around where you want to start learning. Maybe even start a routine if you want to lear everyday!
Start small everyday learn/study for 30 or more minutes and gradually add more time. After that start making learning part of a routine around the same time every day.