I simply accumulated time in and around LT1 pace. Over time I went from say 30-45 min during a 60-90 min ride to upwards 90-120 min. During the week I would also do a hard day. Typically a mock 10 mile TT with friends. My longer rides during the period were around 3-4 hours.
Without being scientific about progressive overload or increasing time in zone each week, I basically just built a solid aerobic base by riding 8-10 hours a week, at least one long day and accumulating minutes in and around LT1.
During that period my MLSS came back to roughly historic highs and my 20 minute power was about 95% of historic maxima. My long rides became very enjoyable as fitness to ride at LT1 and tempo went way up.
I know that’s not a nicely laid out scientific plan but was more like riding each day with a purpose.
Here is a link to a long thread where different riders describe how they have used LT1 data. Along with ways to determine (estimate) LT1 without lactate testing. The magic is really in accumulating Z2 minutes and increasing time in that zone to develop the base. The LT1 twist seems helpful, but might also just be a means to an end.
As we say over here that’s two cents worth of thinking and about a dollar worth of text to get it 