This keeps looping forever even though it's supposed to stop when db_value is 0?

I already fixed this problem when answering your last question, but I don't mind answering again.

You're forgetting to include .Value after the db_value variable on line 3 and line 5.

db_value.Value = db
repeat 
    wait(1)
    db_value.Value =  db_value.Value -1
    print(db_value.Value)
until db_value.Value <= 0
end

you can do this;

db_value.Value = db
repeat wait(1)
if db_value ~= 0 then
db_value =  db_value -1
print(db_value)
end
until db_value == 0 --> This is supposed to loop it until the value reaches 0, right?
end

Instead of using repeat, I'd do this:

while db_value > 0 do
    db_value =  db_value -1
    print(db_value)
end