I need help with coding...

I really have no idea what the question is that you are asking. Can you be more specific?

There is no problem with the code itself, but as I input things like BUTTON_SW and BUS_SW, I didn't have enough buttons in my kit to run the hour, minute, second, and mode conversion…

So I want to allocate BUTTON_SW to work as much as the DIP button in the kit is turned on. But that code failed.

By the way, I would have written your code like this...

always @(posedge CLK_100HZ or negedge RESETN)
    begin
    if (~RESETN)
        DIP <= 1'b0;
    else
        if (DIP < 17) DIP <= BUTTON_SW[DIP[3:0]];
    end

which is much more succinct.

I also prefer to use a non-blocking register assignment (<=) as opposed to a blocking (=) assignment UNLESS you specifically need the functionality of a blocking assignment (ie, if you are computing temporary intermediate values).

And I always put the clock edge first in the always @() block to make it clear what clock edge is providing state transition.