part two! (sorry about that)
Relapses happen. Sometimes all the coping skills we know go out the window. That's okay. You're not back to square one. You've still learned so much, you've still made it so long without self harming. You still have all of those skills with you despite that relapse.
The grounding exercises are sooo good. Have you ever thought of making a self soothe kit? It's like a box with things to help keep you safe, whether it's a safety plan, creams, photos, perfumes/smells, something to eat/drink.. Especially anything that feels sensory (sight, smell, touch, sound, taste).
I hope this helps a little. Keep going, you've got this.