You make progress on day 0. The day after you relapse. Not on day 5, 10, or 99. Those aren't real progress. What do I mean?
Day 0 is the day you have a chance to learn from your mistake. Its the day you can actually introduce new safe guards. It's the day you actually improve. Don't waste your Day 0's on shame or sorrow. Feel bad long enough to recognize you screwed up and to keep yourself humble. Then set out determined to improve.
Learn. Why did you relapse? What were you feeling? Excess stress? Anxiety? Depression? Did something trigger you? If so, how can you avoid those triggers in the future? Do you need to give up social media, or your favorite TV show? Do you need to take up a new hobby because you have too much idle time? Learn. Learn, learn, learn. Do not waste your day 0. Use it for all it's worth. Analyze your emotions, behavior, surroundings, everything. Then adjust your approach and improve.
Stay determined and good luck.