When you would normally roll one or more dice to restore Hit Points to a creature with a spell or Channel Divinity, don’t roll those dice for the healing; instead use the highest number possible for each die. For example, instead of restoring 2d6 Hit Points to a creature with a spell, you restore 12.
RollQuest ships the D&D 2024 SRD as a content pack, on a 5e character sheet that does the maths - roll from the sheet and let the numbers work themselves out. Free to start.