How do I build routines without relying on constant willpower?

Routine-building often includes a schedule. Many people who struggle with willpower need to start small, but a calendar with written plans is a low-effort start. Even without fixed routines most people drink a coffee or tea around the same time everyday and you can use this cue to help build. Answering important emails while drinking your coffee can be a quick start. For all tasks it can be helpful to link things together. Take what you currently do on a regular basis and try to attach it to things that you know you need to do regularly. Over time you expand on this to include scheduled exercise, work-time, errands, etc. Sometimes tying in rewards like a 15 minute break playing a game on your phone, or scrolling (whatever you enjoy) whenever you accomplish the errands that you most dread. People respond well to rewards and eventually these tricks become habits. The most important thing is not to let yourself get discouraged if you "fall off the wagon". Just re-start the habit and move forward.