Thanks for posting my article.
In your case, just break down the lunge, before actually performing the enture movment.
1.) Work on ankle mobility/calf flexibility
2.) Foam roll hip flexors/quads
3.) Stretch Hamstrings/adductors
4.) Strengthen glutes and core
Work on those steps and then begin with my
Stand to Sit drill that I included in the article. From there progress to a split squat or stationary lunge exercise. Then from there go to backward lunge and finally, forward lunge.
ETA? Give yourself about 2-3 weeks..depending on your adherence and frequency.