If this attribute modifier is for the player item, ofc they will constantly die.
Do you have a command to set it back to at least 0? (Can't just set it to 0, you need to /replaceitem the item with a new one on the players' slot.weapon.mainhand or whatever slot you use to let the player hold the item.)
One way to fix this is to go to your server properties file and disable command blocks. Log into to your server and you can ctrl+middle click to copy the Repeat Block to keep on your hotbar. Break the Repeat Block.
Then you can re-enable command blocks in config and set that Repeat Block back after fixing the buggy portion of your command.