How can I decrease the health of an item by 1?

Solution 1:

There's unfortunately no way of decreasing NBT tags with commands. You can only set them.

You can however do this:

The NBT tag {Health:Xs} acts just like hearts, and the item dies just like a normal player does when it hits 0. You can spawn the items on fire and set the health value to the amount of seconds you want the items to last.

Example:

summon item ~ ~ ~ {Item:{id:"stone",Count:1b},Fire:1200s,Health:60s}

The item I just summoned with this command will last for 60 seconds total. The NBT tag {Fire:Xs} works with ticks. And fire takes 1 value off the Health NBT tag per second. Meaning the item will die in 60 seconds. (1 second = 20 ticks)

Hope this helps!