run the /function attribute:uninstall to remove the scoreboards and storage data.
add value
/function attribute:modify {attribute:"generic.max_health",value:10}
remove value
/function attribute:modify {attribute:"generic.max_health",value:-10}
works with all attributes(haven't tested them all, but it should)
works up to the 6th decimal
/function attribute:modify {attribute:"generic.movement_speed",value:0.000055}