Go to Settings → Custom tag categories. There are lists for practice types, state tags and day-level tags, plus your Daily Log sliders.

• Add: type a name and press Add.
• Rename: press the pencil. Every past entry that used the old name is renamed too.
• Delete: if past entries use it, you choose whether they keep it, lose it, or have it merged into another tag.
• Signs (+ · −): tell Insights whether a tag or slider is good, neutral or hard.