Slo-Mo Slice has no login. You can remove data in two places:
Uninstall the app, or clear app storage in Android / iOS settings. That wipes the local save (progress, coins, scrapbook, nickname copy on device).
Email support@slomoslice.online with subject Delete Slo-Mo Slice rank and include:
We will delete the matching Cloudflare rank row. We cannot restore a wiped device save.