Datapack to change your health amount to whatever amount you desire it to be!
Custom health or custom hearts, 2 HP is equal to 1 heart, but it will work even if you use hearts which aren't multiples of 2.

To alter the hp value you want players to have follow this steps:

1. go to data/customhp/functions/

2. open the .mcfunction file with notepad/virtual studio code/any other code editting software

3. change the value in
"attribute @p[tag=chp] minecraft:generic.max_health base set 40" from "40" to your desired amount of HP in integral numbers!

4. load the datapack, and the players HP will change to that amount!
This datapack will affect any players on your server.